If your goth boy is going to wear eyeliner, make sure he wears waterproof brands. Goth boys take their vamp delusions rather seriously and may not understand why you are laughing hysterically at their ghoulish goals. Be prepared to play a role playing game many a Friday night. Watch where you step in his bedroom. Goth kids love to keep tarantulas and other creepy crawlies as pets.
Black cats are also a favorite.
If he has Sea Monkeys, he's a fake. If he's prettier wearing your black dresses than you are - get another boyfriend. You don't want to be the ugly one in the relationship. Check out his bookshelf to see what he reads. Don't be shocked if you see The Hobbit sitting right next to a book by Anton LaVey.