Alex Trebek Calls Contestant a Loser on 'Jeopardy!'

Who knew Alex Trebek was a trash talker?

The "Jeopardy!" host blasted a contestant in Wednesday's show because of -- get this -- her taste in music. Check out the vid ... Alex gave her full-on Trump treatment.

BTW ... the woman is Susan Cole, a legislative librarian from Bowie, Maryland. And she scorched the competition ... taking home a cool $22k.