Unlike a normal bitch, this type of female is the lowest of the low. This term is meant for a ugly, skanky, trashy bitch that thinks that she is the shit, but really is just hot garbage. On a scale of 1-10 (10 being highest), a garbitch is a -2.
(Note: Garbitch can be used as a noun or as an adjective)
Dude #1: If you were stranded on an island with Tara Reid and you got horny, would you do her?
Dude #2: LMAO are you serious? Hell no! That bitch is trash!
Dude #3: Yeah dude, she's a garbitch