Bitch

Someone (typically female) who talks about others behind their back, or goes from one major emotion or personality to a totally different one in practically no time at all. A male variant is prick, though both terms can be used to describe anyone.

Bitch 1: Oh my god! Beth is so stupid. She's the only one who failed drama, and I bet she doesn't even know how to spell orange.

Bitch 2: Come at me you psycho!

Rando: All right then, hold still, this'll only hurt a lot.

Bitch 2: Omg! Mrs. Blank, Rando is picking on me! *fake-ass crying*