look up any word, like fellated:
 
1.
cool; be on top of things; in the know; in with current styles or trends.
"Tyrell has one hella nice new Escalade!"
-"Yeah, that boy's always with it."

~or~

"I'm so freaked out about this date."
-"Dude, will you just get with it?"
by Vesuvius October 13, 2006
 
2.
Contemporary,cool, hip, hep, in the know
He is really withit.
by Felipa Richland April 26, 2005
 
3.
To agree with;
Andy: I'll be at the batting cage at 6 o'clock, you still going?

David: With it, Pal. Count on it.
by js83 March 25, 2014