Can someone please tell me why I can't block a certain friend from seeing tagged photos on facebook?

Basically what I'm trying to do is keep my little cousin from seeing some of the more "inappropriate" pictures I'm tagged in on facebook. Basically he doesn't need to see me at parties with a beer in my hand or anything like that. I know there is a privacy feature on facebook where you can block certain friends from viewing certain albums, wall posts, tagged pictures etc. I have most of my family blocked from my tagged photos but when I try and type my cousins name into the block box it doesn't show up and it won't let me block him. Can anyone tell me why this is and what I can maybe do about it?