Having attraction to multiple males -- sometimes several at once. Someone who is boy crazy will typically admit attraction to most males who enter their life at some point. The attraction is usually mutual but brief. The boy crazy person changes his/her mind about the boy(s); and the boy(s) that are subject to said "crazy," usually have either no interest in someone that is boy crazy, or has gotten what he's wanted and moves on. "Boy crazy" is often taken as an insult.
"Yergachef called me boy crazy and it's not true.
Their evidence was that I have one or more new love interest each week. That may be true, but it's not fair because my new love interests don't work out for any number of serious reasons. So I move on. That's hardly what I would call boy crazy. It's just that I missed out on dating as a teenager, and I have to make up for it." (Yes, she is boy crazy).