A colloquial expression used in simile-like grammatical constructions to attribute particular force to the action of a verb. To state that something is happening "like nobody's business" suggests that it is happening with a particularly high degree of intensity.
It's raining outside like nobody's business!
by Sam Sundquist June 18, 2005
by Sunshine1975 January 6, 2011
by Breaking dancing on cardboard December 9, 2020
My little brother can pitch like nobody’s business. He struck out 6 batters in a row in the game yesterday.
by Breaking dancing on cardboard July 15, 2021