How did he get the weed off you? Did you just hand it to him or what? I used to let people take stuff off me when I was younger, not any more though. If he tries shit like that again punch him in the throat, even if he's bigger/tougher than you. He may beat your arse for doing this but he'll be less likely to take your weed again because he knows he'll have a fight on his hands. If you just keep letting him take it and making it easy for him he won't stop doing it. Go for the throat!