Beyonce Got Slapped On Her Behind By A Fan At Denmark Concert.

Beyonce was too damn bootylicious for one fan in Denmark ... who reached up onto the stage and slapped the singer right on her ass during her concert last night.

Mrs. Carter was performing "Irreplaceable" at the Forum in Copenhagen ... when a dude with front row seats lunged on to the stage and delivered a full 5-fingered smack to Beyonce's left butt cheek.

Beyonce was PISSSSSSED -- she stopped dead in her tracks ... stared at the guy and said, "I'm gonna have you escorted out of here."

It's unclear if she followed through on her threat.