How is your GF's parenting? If there is one 'good' kid and one 'bad' kid, does she treat them differently? Is their bio-dad in the picture? Sometimes kids go through phases...you said yourself that he seems better lately. To save your sanity, you might have to let some of the annoying things go. Choice your battles. He should NEVER be putting his hands on your son in anger, but the 'smell my butt' comment is common for kids that age. Talk to your GF about your parenting styles. Make sure you are on the same page or else you are in for a bumpy ride no matter how much you love her.

So your problem isn't the 5 year old. It's your girlfriend. If you are the first person in this kid's life to correct him, then your gf is doing a bad job of being a parent. She needs to step up and control her kid. It's strange she would have two so wildly disparate children, but stranger things have happened. Maybe it's guilt, maybe it's that he's her baby, I don't know.

But the deal is you aren't daddy to this kid so mom has to be the one to deal with this. As he gets older he will resent the ever loving day lights out of you if you are the disciplinarian and mom just stands back allowing whatever. That very well could put your hope of a blended family straight in the trash. Mom needs to be the lead on the discipline, have the heavier hand in assigning punishments.

You may also want to look at your type of punishment. Grounding a five year old sounds a little odd to me. What about time outs or removing the toys causing the problems? Little kids don't equate long punishments well with the actual behavior causing the problem. Make him apologize, lose tv for the night or dessert or something.

It's also possible that he may have something like ADD if his normal state is Tasmanian devil. Might want to get him checked.

I have a 5 year old, and I know a LOT of 5 year olds. I'll tell you that your SS5 is normal, in terms of his sense of humor and boundary pushing.

The problem is actually your GF. The kid throws a fit and she... .REWARDS him for it?!? No no no - that is bad parenting.

So there's good news and bad news. The good news is that your SS5 is a normal kid and is perfectly capable of behaving better. (Not perfectly, of course, no kid is perfect. But MUCH better.)

The bad news is that in order to accomplish this, your GF is REALLY going to have to step up and be a parent. She's going to have to say "no" and mean it, and stick with it. She's going to have to have certain expectations of his behavior and actually implement consequences if the kid doesn't meet those expectations. I see that YOU are doing that (yay, you!), but Mom absolutely has to do it too. Because if Mom keeps giving in to tantrums and not actually parenting her kid, that poor kid is doomed. She's going to ruin him, and likely your relationship in the process. Read some of the threads around here on out of control teens - that's where you're headed if Mom doesn't knock off rewarding poor behavior.

I didn't need to get past the shopping cart but I did. It's your girlfriend's fault. Yeah, the perfect woman who you love oh so much. She's giving in to the kid and not disciplining him because it's easier for her. She created the monster and she's encouraging it to get worse.

Yall have different parenting styles. Doesn't mean you are right and she is wrong, just means you two are different. She absolutely has to be the one to take care of SS5's attitude.
The more you try to force your parenting style on her kid the more that kid will grow to resent you. There's been days when I've wanted to throat punch my SD and one of my SS's, but I don't. You constantly yelling at the kid probably has something to do with his acting out. Believe me, I understand the wanting to yell and smack but you have to understand that he isn't yours to yell at or smack.
How would you like it if you found out your sons SP was yelling at him?
You need to have a talk with your gf away from the kids and explain that he is doing this...and you want her to step up and correct his behavior. She has to be the one do it.
I've yelled at my SD two or threes times, and each time my DH acts like I punched him in the junk for no reason. If I value my relationship with my DH, I can't yell at his kids no matter how dispicable they are. So, I have to get up and leave the room, or the house. Just ignore them. I make sure he does it all with his kids because I'm tired of dealing with it.

Lots of good advice above. The only thing I have to suggest is to get the 5 year old back in a 5-point harness seat. My kids were in them until about age 7. They are actually more comfortable because they fit a child better, even though no kid really likes the restraint. One thing that drives me batty is parents trying to push their kids out of appropriate seating in the car because they are "sooooo grown up..." They are putting them in danger.

I know that my own DH was the "trouble maker" child in their family. Turned out that probably 80% of the behaviors that drove his parents crazy (and his dad to beat the ever loving daylights out of him on a regular basis) were probably because he has ADHD. He never got diagnosed until he was an adult because he did relatively well in school, besides being a major distraction to other students.

He still has a lot of anger inside for how he was treated as a child.

Maybe suggest that you both attend a parenting class or counseling to help solidify how to deal with all the children. You cannot have two that are let do what they want and one with rules without the one getting very resentful over time. You need to have a unified front and that includes parenting.

The French have WAY less "ADHD" diagnoses due to the difference in approach. They believe in a cause/effect rather than biological problem. They search for what's causing the instability in the child's life and often it's a family in turmoil and little structure, etc. and they help the parents improve the situation. We have it backwards. We have so many parents that have no clue what they're doing and we want to drug the kids to quiet the "problem."

Does it change your attitude if you think these behaviour problems are more about parenting and the need for structure than they are about the kid being bad?

I *never* yell at my kid. Well, I have when she goes to do something dangerous, I need to catch her attention. But I don't yell in anger AT her.

It's ok to be angry, it's how you express it. Like another poster said, you are a HUGE example to these kids, your own included, so think carefully of the role model you want to be.

Another poster suggested finding ways to prevent the behaviour. If you need the 5 yo to be safe in the car and he's not able to do it on his own, then you create the situation where it's not up to the 5 yo. Back to the 5 pt harness. Same with the toys - you draw a line somewhere about what's ok and what's not. And you decide what the consequences are.

You tell the kid where the line is and you enact the same consequences every time. It's really very boring, because the kid is going to test you 500 times in the exact same way. Something about being a kid - they love the safety of knowing where the boundaries are. I guess they get a kick out of going right up to the edge and putting one toe over every day... and ever single time getting put in time out!

A bonus though is that your patience won't wear so thin. You'll be confident with what you expect and confident with the consequences, so no more negotiating or yelling or any of it.

As you go along, you'll get better at estimating what expectations are reasonable for your kid, and what consequences you're comfortable with in what situations.

As an example, my kid is 1 year old and learning to eat with a spoon. She's pretty good at it, but sometimes she waves that spoon around. First she hears "No, spoon goes in your mouth." If she keeps doing it then I ask, "Are you finished?" and I put my hand over hers to direct her to put it down or in her mouth. If she puts up a fuss, I remind her "Spoon goes in your mouth" and do a spoonful with my hand over hers. If the fuss continues, back to "Are you finished?" and I take the food away. I keep it pleasant and smiley, but it's clear what behaviour is expected and what the consequences are. She can have other food that she can eat herself, just not food that she needs a spoon for.

While eating, she'll sometimes spit a mouthful back out. I say, "No" and maintain disappointed eye contact. Then try again. If it happens again, that part of the meal is over.

Sometimes she'll start blowing raspberries/using her spoon like a toothbrush. This I ignore. I figure I can't address everything at once!

Man, you're describing what my SD used to be and how our situation was.

I first came into the picture when she was 3, almost 4. Very sweet kid, to an extent. Her vocabulary was lacking. And by lacking, I mean her sentences were "Where us are going at?" and her words were almost undecipherable ("star" was always "dar"). She had no manners whatsoever. To DH, this was normal kid behavior. But then I came into the picture with my 2 girls (ages 2 and 1 at the time). Even my 1 year old could say a recognizable "thank you" and "please". DH was blown away. He asked, begged me even, to help him get his daughter that way, and I agreed. But here's the thing: he wanted me to help without him having to change things around. He would literally make her 5 different dinners in one night because she would say something was icky and refuse to eat. He would undermine me as an authoritative figure. He would constantly make excuses for her behavior. Finally, I had enough after an incident with her hurting my kids, and I told him such. He said it was just her being a kid, put her on our bed for a "time out" without explaining it to her, and told me I was overreacting. HUGE mistake. I walked. Luckily, it was the check he needed, and things shaped up really quickly after that. Now, it was rocky, and that first time daddy told his little girl "no", you would've thought Hell was uprising. But now, at 8 years old, my SD is an amazing little girl that everyone is so impressed by. She's smart, polite, friendly, caring, and getting office notes from school about how amazing she is. The only different thing we did? Get on the same parenting page.

ADHD or ADD could potentially be a reason. However, I wouldn't give up on being consistent and united in parenting "rules". You can't begin to imagine the difference it can make. It's hard work, and some nights you scream into a pillow until your face is blue. You'll want to give up, because the kid will test you. But the future is SO worth it.

I don't think the kid is the big issue here. I think it's differences in parenting and lack of consistency.