What is Grumping?
1.
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?
See
2.
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."