I think my neighbor is a drug dealer O_O what should i do?

Every other I see different people drive up in his driveway and rush up to his door and go in without even knocking, then a loud gibber-jabber arguement ensues then the person speeds off manically..The neighbor has lots of tats and always seems paranoid. I once invited him over to a barbecue with my other neighbors and he smelt of marijuana and tobacco and didn't converse with anyone. He just sat alone kinda twitching and drinking a Pepsi looking at us suspiciously. Needless to say i haven't invited him to any other barbecues..