Because they're insecure and want attention - if they can elicit a response from her then a woman has acknowledged their existence. Or because they feel innately that they are superior to women because they are male, and then cant comprehend that she is more prominent than they are, which makes them angry.

Immaturity essentially, given teeth by the anonymous power of the net and some distorted belief in freedom of speech (on the part of the companies that should be excising this crap).