1. slang To lose one's reason or sanity; to become crazy or psychotic. In this phrase, "nut" is a derogatory slang term meaning "a crazy person." All those days of sleep deprivation finally caused him to start nutting up. It seems that the former employee nutted up after being fired and began planning an attack against his ex-employers.
2. vulgar slang To start acting in a strong, confident, and/or courageous manner, especially after having previously failed to do so. In this phrase, "nut" is the singular of "nuts," a vulgar slang term for testicles also used figuratively to mean confidence, courage, bravado, etc. The phrase is not exclusively applied to males. Often used as an imperative. You need to nut up and ask your boss for a raise already! Janet, I know you're nervous about asking Tom out on a date, but just nut up and give it a shot!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
Sl. to go crazy. (See also crack up.) I knew I would nut up if I didn't quit that job. I almost nutted up at the last place I worked.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
1. in. to go crazy; to go nuts. I’ve got to have a vacation soon, or I’m going to nut up.
2. and sack up in. get courage; to grow some balls. Come on, man! Nut up! Stand up for yourself! Sack up and let’s go win this game.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.