I thought it was an expression used only in Southeastern Wisconsin. I moved there from Detroit in 1958, and never got used to the expression - I'd say it just to be funny. Then I dated a woman from Harrisburg, Pennsylvania - and she used that expression. She also said, "The faucet needs fixed," (our Pennsylvania Max says that, too) and we didn't have that expression in Wisconsin.

As leeneia says above, it seems to come from the German verb "mitkommen" - the "mit" being a separable prefix.

-Joe-

MtheGM - while linguistics could possibly not fit into "folklore," we've always classed it under the Folklore tag here - and it stays in the music section, because it's often related to music.