Shouldn't it have been: 't's up bitches?
Also, should he have turned his caps lock off?
Do you really have nothing else to do? In America, the land of Slanglish, convenient English, made up words, terms, expressions from "gonna" to "wanna" to "cuz" to no capitalization nor punctuation, etc. you are asking about this? I suggest you stop taking photos while driving or any other activity not involved in the act of driving, immediately. This is dangerous. The teenager driving this "truck" ran into a light pole that did not move. The pole had been in its location for years.
Sup is a slang contraction for what's up. Surprised he didn't have the naked girl silhouettes on there as well. Tastefull, really showin' some class there as well as a diminished IQ. Did you know it has been proven that for every inch of lift on a truck your IQ diminishes by 20 points?
It means: What's up bitches.
All slang is grammatically incorrect. That's the point of slang.
If a person needs to display such a message; correct English grammar is the least of his/her problems.
Do you really have nothing better to be doing?
yes it is
Saw this pickup on the highway with a back window that had written SUP BITCHES.
Shouldn't it have been: 't's up bitches?
Also, should he have turned his caps lock off?