To be actively grumpy, in such a way that the person in question is actively making an effort to be grumpy and, moreover, express that grumpiness.
Dude: Harrumph. Grr. I'm so grumpy.
Guy: Dude, why are you grumping like that?
The act of making an exaggerated frown in the shape of an upside down "U." Often used when someone is being ridiculed in a joking situation.
While grumping be sure to make your frown as curvy and unpleasant as possible
The act of "dry humping" while grinding on a dance floor.
"Yo, that dude is dancing so hard with that chick he's grumping!"
Johnson's slow, angry and sad behavior when he's grumpy.
"Why does he seems depressed today?"
"He's just grumpy. He does it really well, too. I woke up today, planning to be grumpy, but it just didn't work out."
"Okay, he's grumping his way over; we can leave now."
a sexual practice involving placing your face inbetween the legs of a corpse and getting a partner to jump hard on the corpse's stomach.
Hey Keith, wanna go grumping tonight?