Akademik

Дураку все смех на уме
Fools are always laughing, they are never serious. See Смех без причины - признак дурачины (C)
Cf: It's a trifle that makes fools laugh (Am.). Too much laughter discovers folly (Br.)

Русско-английский словарь пословиц и поговорок. . 2013.