This one's pretty funny. I'm not actually guilty of very many of these. Honest.
Here's a sample:
5. Wearing obscurely geeky T-shirts to "normal" places - Every geek has at least a few of these; don't try to deny it. We love them, because we get the jokes and we know that only other geeks will get them, too. Unfortunately, they can make our less geeky significant others feel a bit conspicuous when out with us—or maybe they feel the geekiness will rub off on them, I'm not quite sure. Still, I feel that if I have to occasionally let my daughter wear a Hello Kitty shirt out of the house, I can wear my shirts from ThinkGeek.
Let's just say I have a pretty impressive collection of library vendor t-shirts and leave it at that.