comes from the verb unce unce unce which is usually applied to a beat of a song. when one feels awkward and has nothing to say just unce. It can mean many things from having sex or getting exciting to go out.
For example, if a friend Liz is having sex with a white rapper, you can say she is uncting with the white rapper followed by unce unce unce.
by intrepid.unce May 04, 2009