Green’s Dictionary of Slang

cheery, slightly eccentric.

1937		J. Tully Bruiser 107: A slap-happy bum.
1946		Mezzrow & Wolfe Really the Blues 76: He was taking potshots at the electric bulbs, with a slap-happy grin on his kisser.
1951		Hastings & St Leonards Obs. 14 July 6/4: They were a little ‘sla-happy about book-keeping’.
1952		(con. 1920s) ‘Harry Grey’ Hoods (1953) 131: They were ten-dollar bill slap-happy. They went into every store in the neighborhood trying out your samples.
1965		D. Pearce Cool Hand Luke (1967) 39: The same horseplay and slaphappy jokes of fresh conscripts going into the army.
1975		W. Trevor Angels at the Ritz 187: She’d been a slap-happy mother and was a slap-happy wife, not caring much what people thought if her child wasn’t as meticulously turned out as other children.
1986		L. Heinemann Paco’s Story (1987) 161: Slaphappy people look stupid, loony — and drivers think you’re on something.
1997		Arizona Republic (Phoenix, AZ) 17 Jan. 54/1: Sla-happy ‘Ninja’ needs less dialogue.
2001		(con. 1975–6) E. Little Steel Toes 62: Couple of slaphappy motherfuckers, giggling like little girls.
2012		Sth Florida Sun Sentinel (Fort Lauderdale, FL) 29 Jan. G11/3: Book Review. Slap-happy spy caper takes aim at Florida.
2017		Maryland Indep. (Port Tobacco, MD) 15 Feb. B16/5: Maybe it was the slap-happy 10 pm clicking around on my smart-phone but I was briefly tempted.