He knows how to lose weight, but he should also learn how to lose the 'tude.

While he was in Minneapolis to make an appearance at the Mall of America, The Biggest Loser's "Bob the Trainer" (a.k.a. Bob Harper) also wanted to make an appearance at Bar La Grassa.

He tried to book a table at 7:30 p.m. with the American Express concierge service, but -- since the restaurant was completely booked --  it had to decline.

"The only way we could accomodate them is if we screwed someone else over, and we don't do that," said Isaac Becker, the restaurant's owner/chef.

In retaliation, "Bob the Trainer" attacked the restaurant on Twitter:

"OMG!! The manager at Bar Lagrasa in Minneapolis was SO RUDE to me. I wanted to have dinner there. Why are people so mean sometimes?" ~Bob Harper

and ...

"And Minneapolis is one of my favorite places...why did the manager at Bar Lagrasa have to be like that?? I still love it here!!:" ~Bob Harper

and ...

"I need @jillianmichaels to unleash on the manager at Bar Lagrasa in Minneapolis. He should be very afraid!!" ~Bob Harper

which led to The Biggest Loser trainer Jillian Michaels' response ...

"I'll go beat him up. What's his name?" ~Jillian Michaels

The tweets resulted in a lot of harassing hater calls coming into the restaurant throughout the evening. It got so bad at one point that Isaac had to sit in the office and field calls -- instead of tending to his staff and patrons on a sold-out Saturday night.

And that is why these "Biggest Losers" are on our "Douche on the Loose" radar.

Grow up, Bob.

And, Jillian ... anger management, perhaps?