A large quantity of something, usu. intended to be greater than hugantic or ginormous but regardless is referring to multiple items or actions.
All right, recruit--I'd better see me a metric butt ton of shoe polish on those boots or I'm gonna rip you a new one!
-or-
I'm afraid I can't join you and the lads for the croquet match today, as I have a metric butt ton of wallhangings to color-coordinate before the Gimp arrives this evening.
Slightly more than an Imperial fuck ton. The exact measurements of the metric fuck ton are unknown, owing to the fact that the term is generally used to describe an indeterminately-large quantity of something.
That pizza you left on the floor last night is now covered in a metric fuck ton of ants.