Terrible twos and then some

So I have a 2yo DCB who has hit his terrible twos HARD.If I ask him to do something, (anything), he growls and grunts at me and starts smacking anything in range like the couch, a toy, his own leg..... If he gets frustrated with another dck he hits them. He has hit and kicked me which is a definite no no. I was chatting with mom at his pick up time and one of the other dcbs walked up to him, and 2 yo dcb slapped him in the face right in front of both of us. To moms credit, she sternly disciplined him right then and there but he just smiled like it was funny. I've tried putting him in a playpen for time outs, (so he can't hit anyone if they happen to walk past him), but he is not "getting it". This has been going on for a few weeks now, and I'm not getting anywhere with him. I love his parents, they are always on board with what I suggest, and I know they are not letting him get away with this at home either. WWYD?

what matters most to him? sometimes time outs don't work for some. I had 1 boy who hated being last at things. If he was acting up then I made him go last for everything. Also when you put him in time out then do something fun with the others that he can't participate in - like coloring or playdough. I have given kids rice cakes for afternoon snack while others get cookies etc. That kind of things. I would still do the timeouts but include something else.