Short for cunt-ass-bitch. This word is to be used against those who one truly despises or hates. When called a cab, one must accept that they have been ridiculed and made fun of far worse than any comeback/retort that they may think of. Cab is the ultimate diss, and inflicts humiliation and embarrassment on those who are subject to being called a cab.
"Marc is a huge cab for not showing up to my birthday party!"
"Rich you're a huge fucking cab!"