I'm a college sophomore, and my boyfriend is a senior. He's a football player, and other girls have crushes on him. Recently, he was with his guy friends at a party. A girl came over and said I'd slapped her across the face. I've never even met her! Why would she do this?

--Mystified

Women are seen as the kinder, gentler sex because they tend not to leave a trail of bloody noses and broken barstools. But women go plenty aggressive on other women, just in ways they can't patch up at urgent care -- like when some mean girl dislocates your reputation and fractures your psyche in 36 places.

In short, while men have Fight Club, women have Underhanded Snipe Club. Researchers find that women almost always use "indirect aggression" against other women -- nasty gossip, ostracism, and "just trying to help!" shaming remarks -- to vie for mates and jobs. Psychologist Kaj Bjorkqvist explains that this covert "social manipulation" maximizes the harm to the victim while minimizing the risk of counterattack on the perpetrator, who often remains anonymous -- leaving the victim unable to trace how her social status ended up in the morgue.

Women's mate competition can be a beauty contest -- hotting up one's appearance to yank male eyeballs away from female rivals -- or an ugly contest: using "competitor derogation" (disparaging the competition to decrease others' mate value relative to one's own). A woman trashing another woman to men typically sneers that she's ugly or slutty (in line with men's evolved priorities for physical attractiveness and fidelity). However, evolutionary psychologist Maryanne Fisher observes that if the woman casting the shade is not all that hot herself, her remarks about another woman's looks are likely to be dismissed. This might lead her to rely on "alternative tactics" -- like inventing a story about how a hot woman is actually the lady bar brawler of the sophomore class.

Unfortunately for the cuckoo case trying to destroy your reputation, her efforts may backfire. Most undergrad guys aren't dating to wife up, so some (or many!) would be way into a high scorer on the hot/crazy scale: Hello, aggro babe hate sex! As for the eventual "auto detailing" that so often comes with, guys try to focus on the upside, like their car being easier to spot in a crowded campus parking lot. (Just look for the hot-pink spray paint, "GET YOUR HERPES HERE!")

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.