I've given blood 4 times.
My blood type is: A RH positive
and after I had sexual relations with another man for the first time, my blood was no longer good enough for them.

A friend of mine once went to give blood at a mobile unit, and the nurse gave her a puzzled look and said she didn't know if she was allowed to take her blood. My friend asked why not, and the nurse blushed and explained it's because my friend is Black that she wasn't sure if she could. My friend decided to save her the worry and left.

Giving blood is a good, helpful thing, but damn, the people who take it from you can rely be jerks about it.