Green’s Dictionary of Slang

1. incompetent, second-rate.

1899–1900

C.L. Cullen Tales of the Ex-Tanks 24: I was the hammiest thing that ever happened.

2. typical of bad acting.

1928		W. Winchell Your Broadway & Mine 27 Nov. [synd. col.] The play [...] is rich with hammy material to please the most [...] stage-struck actor.
1939		New Republic 11 Jan. 281: The acting is consistently hammy.
1946		Mezzrow & Wolfe Really the Blues 139: Some hammy clowning on the bandstand to tickle the simpy customers.
1955		E. Hunter Blackboard Jungle 150: He tried it. A little at a time at first, a few hammy gestures.
1960		J. Havoc Early Havoc 140: She was dragging her feet [...] Much too much I thought — pretty hammy.
1987		B. Chatwin Songlines 104: The two armed themselves with sticks [...] and waved their arms like hammy Shakespearean actors.
1999		Guardian Guide 10–16 July 89: The corny script and hammy acting.
2005		J. Stahl I, Fatty 266: Moulding [the script] for hammy Louie Bartels.
2013		J. Stahl Happy Mutant Baby Pills 142: Susie licked her lips like a hammy porn star.

3. sentimental, false, bogus.

1953		J. Thompson Alcoholics (1993) 31: How hammy can you get?
1955		Mad mag. Aug.–Sept. 7: We’re going to get a little hammy by devoting most our letter column to some of the congratulations.