Definition of "killjoy"

"If you mean me, sir, I call you and every one else to the inspection of my professional life. As to Christian or unchristian, I repudiate your canting palavering Christianity; and as to the way in which I spend my income, it is not my principle to maintain thieves and cheat offspring of their due inheritance in order to support religion and set myself up as a saintly Killjoy...."

1871, George Eliot, Middlemarch

He stalked behind her simple narrative, a kill-joy parent, hasty, intolerant, keeping a special cane to enforce the authority of his sadistic God[.]

1930, Norman Lindsay, Redheap, Sydney, N.S.W.: Ure Smith, published 1965, page 123

Just in time for the party season, some old killjoys at the journal Medicine & Science In Sports & Exercise have released their findings on the effects on muscle of prolonged heavy alcohol intake (six weeks is prolonged, apparently). The bad news is that it seems too much boozing puts all that effort in the gym to waste - in the study, alcohol prevented the usual resistance-training-induced muscle response that leads to increased size and strength.

December 10 2005, Sam Murphy in The Guardian, A sober thought