ahhliss said:
You can find out by donating blood =)
You can find out your own blood type by procuring antigen-binding solutions and a pint of your blood.
Mix the stuff together; check if it agglutinates; if so, then you have the respective antigens, from which you can conclude whether you're A, B, AB, or O, and whether you have the Rhesus factor.
When you donate, it doesn't matter what you have; it does matter, however, when you're receiving. If you receive an incompatible type, happy haemolysis.
At this very moment, I do not receive or donate blood.