@Custos
I guess the reason is that girls are generally more impulsive than guys. If you try hard you will notice that everybody is doing this to some extent. Many times we spew out something before the other persons even finishes his question. ... and then we look dumb. :)
This morning at work I said Brittney Spears was popular because "sex sells" and she said "SHE ISN'T GIVING SEX TO ANYBODY WHAT ARE YOU TALKING ABOUT!?"