Green’s Dictionary of Slang

(orig. US) to act in an exaggerated manner, to ruin a situation by foolishly excessive behaviour.

1914		T.A. Dorgan Indoor Sports 8 Oct. [synd. cartoon] Indoor Sports — Listening to the mothers of the newly married pair ham one another.
1930		Scouting Jan. 17: What you hamming about then? [HDAS].
1947		B. Schulberg Harder They Fall (1971) 305: Stein danced back to his corner [...] hamming it up a little.
1953		R. Chandler Long Good-Bye 66: ‘Jesus, how cheap can a guy get?’ ‘Stop hamming and tell me what you want.’ [Ibid.] 257: Why ham it up any more, Spencer? Paul Marston and Terry Lennox were the same man.
1963		G. Lambert Inside Daisy Clover (1966) 201: You mean I ham it up?
1971		(con. 1950s) J. Brown Monkey Off My Back (1972) 120: Sure enough, the saints did ‘ham it up’.
1983		R. Price Breaks 257: I thought he must be hamming it up, maybe he’s drunk.
1990		R.G. Barratt ‘Bore It Up ’em, Bruce’ in What Do You Reckon (1997) [ebook] This grandstanding old showpony has been hamming it up in front of the crowds.
1999		Indep. on Sun. Real Life 11 July 2: The only obvious fun to be had is the chance to ham it up over the in-flight PA system for the announcements about not smoking or fastening seatbelts.
2000		Guardian Guide 15–21 Jan. 63: One of Britain’s most accomplished actresses coming as near as she’s ever done to hamming it up.
2011		IOL News 🌐 Bad sex — even with its [...] hammed up retellings — is drenched in cold sweat.
2013		K. Sampson Killing Pool 159: He milks it. Either he’s hamming it up or he’s still hoping the elusive tenner [...] will materialise.