Porn could be a surefire way to go
www.giftsyoucangive.com is a completely useless website if you're looking for gift ideas for people under oh, 65. Somehow I rather doubt that my cousin Harold - who turns 30 in a week - would appreciate things like life insurance or a gift voucher for dentures.

Though of course if he had denture fetishism it would be a breeze.

I guess the theory that the better you know someone, the harder they are to buy for isn't entirely baseless.