To compare hand and finger sizes, leading to the comparing of other certain extremeties. This is a command given by one who is insecure about his manhood, and wants to reassure himself that he is as normal as anyone else.
Travis: "Size it up!"
Todd: "Stfu Travis."
by Lee Brody March 11, 2009
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when someone wants to fight you and to basically get on their level; usually said by someone bigger to someone smaller (in height)
boy: I know you aint messin' around with my girl
2nd boy: wanna fight me for it? let's go, size me up!
by private.school.h0mboi February 4, 2011
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The act of checking someone out to see if you can take them in a fight
Chad told me he was sizing up brad and he thinks he can take him.
by DomToretto July 18, 2021
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He did size up the potential destruction, but did not act decisively in the end.
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The phrase "size up", usually used in arguments, essentially means to "stand up and fight"
"Yo, no long talkin' b. Either size up or nize up"

In other words...

"Hey man, I don't want to do this long talking business anymore. Either stand up to me and let's fight, or shut up."
by suwayy March 15, 2017
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The act of looking at someone and determining if you could take them in a fight.
Conor was sizing up Jake for their big fight and thinks he can win.
by LordFarquadd July 25, 2021
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To get a feel of someone's strength by observing them or a call out to get someone to fight you

This pretty simple term which was then redefined by tiktok idiots into: When a man looks if his dick will fit by checking out a girl's thighs.
Bro 1: Bro, I fucked your mom

Bro 2: Size up, bitch.

Bro 1: Bet

What tiktok idiots think it is:

Girl: OMG you're so gross, why are you sizing me up?

Boy: Umm... I wasn't. I don't want to fight
by NNatty August 14, 2021
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