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!
2nd boy: wanna fight me for it? let's go, size me up!
by private.school.h0mboi February 23, 2011
Get the size me upmug.