Mcchillin is when a bunch of teenagers usually loiter or hang out at a McDonald's usually for long periods of time or on a daily basis
Bryan: Hey, what are you doing after school?
Jake: I'm Mcchillin with Stephanie and Mike.
McKing is usually when a person stops at a McDonald's and Burger King due to extreme picky eating.
Boy: Dude, you still McKing?
Girl: I can't help it, Burger King has great burgers and McDonald's has kick-ass fries.
a person who is extremely cranky or crabby on a wednesday morning
girl: Hey whats up?
Guy: ( turns and gives the evil and eye) F off I didnt get enough sleep
Girl: jeeze are you a little cranky wednesdier
Mcgrub is any food, snack, or drink from McDonalds. usually refers to food
Guy: Man, I'm hungry.
Chick: Let's go get some Mcgrub.