thigh-slapper

[ thahy-slap-er ]
/ ˈθaɪˌslæp ər /

noun Informal.

a very funny joke, remark, story, or incident.

Origin of thigh-slapper

First recorded in 1960–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019