Usually uttered by some ultracool individual who is grimly determined to do something unpleasant or difficult, but necessary. First heard by me on “The Simpsons,” in the episode spoofing “Behind the Music,” in which one of Bart’s posse utters those deathless words.
But who said it first?
Phrase that appears on Usenet in the 1994-96 period. Don’t know if that helps.
I don’t know if he’s ever posted to Usenet, but Kevin Spacey said “Let’s do this thing…let’s finish it” in Swimming with Sharks (1994).
Gary Gilmore, the first convict to be executed in the USA after a long hiatus in 1977, had as his last words: “Let’s do it”.
It’s been a standard mob movie line for a while it seems, but I don’t know the first use of it in a mafia setting. It’s almost always used to be a euphanism for killing somebody without saying it, but everybody knows.