Green’s Dictionary of Slang

1. (orig. US) the last, most problematical piece of information.

1950		R. Starnes Another Mug for the Bier 106: The kicker, of course, was the station wagon [...] who ever heard of having a station wagon without painting a coy name on the side of it?
1974		R. Stone Dog Soldiers (1976) 238: And the kicker is—he was never there.
1978		J. Webb Fields of Fire (1980) 358: Then there had been the kicker. ‘I can’t understand how someone could stand by and watch this happen.’.
1988		Eble Campus Sl. Oct.
1990		S. Morgan Homeboy 152: And here’s the kicker [...] this Arkie bohunk named Hutchinson actually [...] helped himself to some of that boy’s butthole.
2023		(con. 1962) J. Ellroy Enchanters 76: ‘You want the kicker? Deedee’s enforcer [...] playing the role of the irate husband, is her real-life brother’.

2. a culminatory action.

1951		M. Spillane One Lonely Night 80: Maybe they were playing real cute and sent her in for the kicker.
1977		E. Torres Q&A 63: But the kicker is, while I was in the courtroom, I had this South American lady client waiting [...] She said, ‘Does this happen often in American courts?’ How do you like that shit?
2001		J. Stahl Plainclothes Naked (2002) 69: The kicker came at a dinner party Marge dragged him to.
2006		G. Iles Turning Angel 147: But the real kicker [...] is that she didn’t just call him direct.
2010		K. Richards Life 431: I said [...] Your sister will hate you forever. He threw in the towel. I knew that was the kicker.
2018		(con. 1963) L. Berney November Road 4: The art of the payoff. Guidry understood each man’s price, the right kicker to close the deal.
2023		(con. 1962) J. Ellroy Enchanters 39: He’s going There, there. Here’s the kicker.