What is Sup!?
1.
Sup! is a greeting/verb. It defines meeting a female talking to or boning her.
Hi grandma! I sup!ped the shit out of this chick yesterday...she was good! Sup!
See
2.
the greatest manga that has ever existed.
"Hello thar, Phil! did you buy the latest volume of Sup!? I hear Sup proposed to V-chan!"