Deb - Yeah it probably wasn't very good training to laugh so hard at him but its just one of those moments when laughter is more appropriate than anything. Kind of like when your kid poops in the bathtub and gets scared of their own turd - you really just can't help but laugh. Luckily, he hasn't stolen my phone again.
I know what you mean about him thinking its all fun and games, though - my sister can't stop laughing when he's biting her and so he thinks its ok. (she's 15 so don't feel bad for her, lol) I've told her that until she stops laughing and gets stern with him, he's gonna think its a game.