Tenacious D -- Concert Shut Down ... Due to STABBING

"I'm gonna hump you sweetly," is not what the crowd at a Tenacious D concert got to experience last night ... because a brutal fight broke out instead and at least one person was STABBED, this according to local reports.

It all went down at Mandalay Bay's House of Blues in Vegas. Jack Black and Kyle Gass were playing a set when all of the sudden a fight erupted in the crowd, according to 8 News Now Vegas.

According to the report, one person was stabbed in the leg and rushed to the hospital, but is expected to recover.

Following the incident, the police shut down the House of Blues, thus cancelling the rest of the concert.