A triple contraction of "you" "all" and "are"; like "couldn't've, shouldn't've, wouldn't've, etc." Used mainly by native Southerners, good way to identify a nativeSoutherner.
"Step off." though far less intimating. Really should only be said as a joke, and only with a horrible ghetto accent and (in)appropriate head-bob + finger-wave combo.
"That is one skanky skirt, sister."
"Yo bitch ya'll best be steppin'."