What makes a geek giggle?

From 10 annoying habits of a geeky spouse:

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 myshirts from ThinkGeek.