When you have sex with a fat male lorry driver from behind, but instead of actually inserting the penis into the anus, you just thrust your penis back and forth within his arse crack, using his sweaty butt cheeks to stimulate yourself.
"I'm not ready for anal just yet, would you mine if we had a go at grutting instead?" - Fat Lorry Driver
"I tottally grutted that guy at the truck stop last night, it was rough as fuck" - Guy who fucked Fat Lorry Driver
1. Gretting
Magical jubilation involving all mythical characters ever known including Santa, Easter Bunny, Leprechauns and more. Often includes a jig, perhaps in the bathroom, while listening to music and gretting simultaneously.
Getting In There with someone, which is where the GIT is derived from. Can be used in a normal conversation between people and other people will not realise what is being said.