"The one serious conviction that a man should have is that nothing is to be taken too seriously."
-- Samuel Butler

"Only the insane take themselves quite seriously."

-- Sir Max Beebohm

"Be sincere, but don't be too serious -- at the last, nothing much matters."

-- Elbert Hubbard

"Not a shred of evidence exists in favor of the idea that life is serious."

-- Brendan Gill 

"Anything worth taking seriously is worth making fun of."

-- Tom Lehrer

"Seriousness is the only refuge of the shallow."

-- Oscar Wilde