Get him a pregnancy test. When he says, ok haha now where my real gift, start crying and yell "you don't like it?"
i'd saya cheep tie from liek sears or macy's or something liek that. a 15$ tie if well picked can look like a 50$ one. either that or some used condoms.
get a gift card for a nice store, put it in an anvelope and say "its a gift card at <insert>, and i think you will be pleased with the surprise" then he thanks, opens it, and when he realises it says nothing on it you slap him in the face and scream: "I DONT LIKE YOU BITCH LOL PWNT" and run away
A chocolate penis. Then write a card saying "It's alright about your sexuality, but please don't try to get in my pants again... Love, your nephew blahblah" All the laughs and smiles will be amazing!