In "Friends", season 7 episode 1 (2000), Joey, who is 31, wants to look and behave like a nineteen-year-old for his audition and uses "'sup" and "whack" in dialog with Chandler (from IMDb):
[Joey comes out from his room wearing ridiculous clothes. He has to look nineteen for an audition]
Joey: 'Sup? 'Sup, dude?
Chandler: [putting his hands up] Take whatever you want, just please don't hurt me.
Joey: So, you're playing a little Playstation, huh? That's whack. Playstation is whack. 'Sup with the whack Playstation, 'sup? Huh? Come on, am I nineteen or what?
Chandler: Yes, on a scale from one to ten, ten being the dumbest a person can look, you are definitely nineteen.
I understand that Joey is using (or trying to use) teen slang. But was this slang used by teens in the late 1990's or was this slang that Joey used as a teen (e.g. about 15 years earlier) and thus making him looking more ridiculous?