Alex Trebek CUSSES -- S-words for $200!

Alex Trebek said the word "sh*t" ... ON CAMERA ... and it's HILARIOUS!!!

America's favorite game show host was leaving Boa steakhouse in Hollywood last night when the valet had a mix up and almost gave his car to somebody else.

But Alex quickly noticed the problem ... politely handled the situation ... and then gave TMZ some Forrest Gump-ian advice -- "Harvey, sh*t happens."

For the record, the "Jeopardy" host suffered a heart attack earlier this year ... but judging by the clip, he's feeling saucier than ever!!!