It's pretty much that he wants to play his way or not at all. We talk about how to play nice and how to make friends and while he's gotten better and is able to play with his younger sister, he still has trouble with kids in his neighborhood. For example, if he's at the pool and there are a couple of kids his age and they all race their cars across the water, he will cut them all off and splash them (not on purpose, but that's what happens as a result) until they leave. He's becoming that "annoying kid" that no one wants to play with. Unfortunately it's hard for him to understand the value of friends and why he should want to be nicer. To him, it's a matter of playing the way HE wants to and he sees nothing wrong with that.
As for playing rough, he saw a bumper cars at a fair and now everything with his matchbox cars and trucks is about smashing them together. This has spilled over into when he rides his big wheel and he'll smash into other kids. Doesn't matter if you warn him, put him in time out, etc. He SAYS the right things -- parrots them, really - about why he shouldn't do that, but it's like he just doesn't really care. He'd rather play with his sister or Mom or any of the adults around.
His parents go between intervening when his play with other kids goes downhill to letting the kids handle it. When the kids leave him to play elsewhere, he's heart-broken and sobbing. They talk about how to change that behavior, but it's like the lesson doesn't carry over to the next time.
Any suggestions on how to teach him to be a friend to other kids? Or is there a discipline more than "time out" that will help?