Homie, it's really straightforward. Women are violent, and homosexuals are more violent than straights. Ergo, homosexual women are absurdly violent. Not to mention they're fucking crazy to begin with. They're just more prone to hit each other. Women fight each other all the time anyway (just look at all these ghetto fights). Adding romantic/sexual relationship dynamics to it is just begging for more violence.
The fact lesbians beat the living shit out of each other with alarming regularity just punches holes in that whole "oh women are super sweet innocent little flowers who wouldn't hurt a fly" narrative and makes them very uncomfortable when you point it out (sometimes violently so, which makes it really funny since they're proving your point).