Mancing is a man dancing by himself. This often occurs at home when no one else is around. Most mancing will involve wearing just underwear and socks but not necessarily limited to just undergarments. It is completely possible for mancing to occur in public and anywhere.
Marc: I love it when Tom Cruise starts mancing in Risky Business.
Zach: That's the only reason to watch that movie!
Joe: You're both gay.
When at a club, a group of three or more males proceed to dance in a man circle to potentially attract females to dance with.
Unlike its origin "mancing", this takes place in public at bars, clubs, family parties, etc., and usually takes the shape of a circle with females usually within close range.
Common cirlicular mancing songs: All techno, "Free Falling" - Tom Petty, "Sweet Caroline" - Neil Diamond.
Applies specifically to the region on Manchester, New Hampshire (not Manchester England). Most directly translated refers to the act of shoving ballon animals filled with black tar heroin into one's rectum.