'Gregging' is the process by which an individual masturbates into a hat. Though this is its definition, it can also be used to describe an individual resting his penis in a hat, and/ or using the hat to masturbate. To 'Greg' someone is to steal their headwear, and perform one of these heinous acts using it.
Example 1)
It has commonly been used to make amusing adjustments to songs:
"Gregging,Gregging you... filling up your beret with my penis"

Example 2)
Ray: "Man, what the fuck is up with your hat?"
James: "you wont believe it, Some punk gregged it last night at the party!"
Ray: "Ouch, dont worry about it, weve all been there before"

Example 3)
Mark: "Hey, look at that blokes hat, you want to greg it?"
Bryn: "Hell yeah!, ill go first"
30 minutes later
Man with Hat: "Bollocks"
by Portlypeasent February 26, 2009
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when a man grabs another man's penis and then tries to rationalize how he is not a homosexual
by Aman5 November 1, 2020
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Dora-"I was Pegging Greg last night with a 12 incher"
John-"So you were gregging him?"
by Cabana man September 2, 2017
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To update your Facebook with 30+ updates/links in an hour, usually music videos and posts about how bored you are.
Greg was totally gregging on Facebook last night - he posted 15 Miley Cyrus videos, 10 ABBA videos, and wrote 15 statuses about how much he loves Justin Bieber's hair.
by Chris968 September 26, 2011
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Taking pictures of your penis in a cabin full of people whilst at camp.
Greg was Gregging so hard that you could see the flash of the camera.
by Daniel Jenson August 6, 2016
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The act of pursuing straight men, as a gay man.
A homosexual saw a handsome straight man walking by and follows along trying to get into the "friend zone" only so that when they go on an overnight trip he can jump on that mans ass!

Guys best friend: Dude, he is so gregging on you right now.
by ADFHFD March 8, 2010
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A term used to describe going to the bakery 'Greggs' and buying food for a meal or snack
Mikki: "Hey, Binks! You gregging for lunch today?"
Binks: "Nah, I'm going subway!"
by Aries-Chan November 6, 2009
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