killjoy

noun1

1. •
   A person who is anti-fun, or prevents others from having fun.

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