"AF" just comes across as childish. Huge turn-off when I see an adult use it.
"I can't" and "gives me life" are ones that are the worse, mostly because they're probably more likely to be spoken aloud and people OD with them.
It's one thing to use slang ironically or to be funny. I'll use "it's lit" when I'm out with my friends and some EXTREME fukkery happens, something AMAZING happens unexpectedly, or just to troll...
*Family gathers around the Christmas tree and lights the decorations*
*nudges girlfriend*
"It's lit."
"I hate you."
*goes to impromptu Hollywood party*
"Special surprise DJ......JUST BLAZE, y'all."
"Wha- oh shyt. It's lit."
*Slow night at the bar. Bartender cuts drunk lady off and she & her boyfriend get kicked out right as she's trying to get her slurred two cents in*
"It's lit." :lupepopcorn:
...but when you get into a conversation with someone and they sound like they only function conversationally through buzzwords, it's a HUGE turn-off.