Phillip Seymour Hoffman's "job" in Punch Drunk Love

Have seen PDL approximately 8 trillion times and still have no idea where Mattress Man is supposed to be in that first scene (chinese restaurant? venue?) ("You can't do that! Its wrong!") or why he's watching a rock band rehearse lol I guess the implication is that he has multiple business ventures underway but I love that the fact he is also a music/event promoter is in no way explained or elaborated upon