I'm thinking that if he really behaves like an a$$ and reacts ungraciously to any little celebration you put together, don't take the bait and get mad-- just say you didn't do it for him, you did it for YOU... you wanted to celebrate his birthday because it felt good to you to do it. Don't argue with him or defend yourself. Don't jump in to the mud pit. Gosh, I hope he's grownup enough to react nicely...