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9.
v. To ejaculate. Literally, when one's testis climb to a "high & tight" position just before launch.
Al was about to nut up when her cell phone rang, turning his hard tool into a soft accessory.
by R2dad August 01, 2006
 
1.
suck it up, just do it, who cares
Dan, Jay and Jeff came out of the corsey and saw some hot girls. Dan and Jay said "hi!!!111oneone" and Jeff said "nut-up!" The girls drove by and flipped us off.
by dFecT June 02, 2004
 
2.
hybrid cross between "grow a pair of nuts" and "man up"
Guy 1: "Oh man, I totally wanna bang that chick over there."

Guy 2: "So nut up and do it already!"
by LOVEMESOMEURBAN October 15, 2010
 
3.
(v.) To gird ones loins. Nutting up entails using one's proverbial balls or "nuts". Mainly used on the US west coast, it's the sister (brother?) term to cowboy up.
I better nut up or I'm gonna get my ass kicked in this fight.
by Neilmiser May 14, 2004
 
4.
Verb phrase: To involve oneself in a physical altercation, to lose one's cool, or to fly off the handle. A common fixture of urban or "gangsta" vernacular. Recently popularized by a homophobic, black-clad drug-dealing NPC/pedestrian in the controversial PS2 game "Grand Theft Auto: San Andreas."
"Yo, I'm fidd'nduh nut up in a minute!!!"
by Buddy-Rey November 07, 2005
 
5.
n. - an unfavorable or adverse situation
My teacher gave us detention - yo, that's the nut-up!
by "Cool Aaron" Taylor October 26, 2007
 
6.
To suddenly go crazy with no apparent provocation. Especially true with emotional issues that have not been previously resolved but avoided.
"I was talking about waiting another year to get married, and she began to nut up on me."
by CWB August 27, 2005
 
7.
to take one for the team, against most odds, to guard closely (in athletic contests) commonly yelled at Ultimate Frisbee games
Yo Bill, nut up and be my wingman tonite

Nut up on that girl, she's been owning you all day
by Texas August 29, 2004