That was fast ... a rookie news anchor in North Dakota has been fired before he even started ... less than a day after dropping an embarrassing f-bomb on live TV.

The anchor's name is A.J. Clemente -- and you have to see the footage, which aired yesterday ... his first day on the job. It's incredible. Not only does he cuss on the air, he also plain sucks.

And A.J.'s superiors didn't waste any time cutting him loose -- he tweeted this morning, saying he'd been canned over the flub. He wrote, "Rookie mistake. I'm a free agent. Can't help but laugh at myself and stay positive. Wish i didnt trip over my 'Freaking Shoes' out of the gate."

Welcome to the viral video hall of fame, pal.