Steve Harwell

The lead singer of Smash Mouth lost his cool during a concert, and started cussing like CRAZY at the crowd ... all because of a little bread. The '90s band (still working the county fair & festival circuit) was performing at a Colorado food fest on Sunday when people in the crowd started throwing…

Smash Mouth frontman Steve Harwell is gearing up to chow down roughly 1,800 calories in one sitting -- promising to polish off 24 EGGS ... if fans throw down $10,000 for charity. A rep for the band tells us the egg stunt wasn't Steve's idea -- that honor goes to a creative fan who posted the…