Dierks Bentley -- Drunk Fan Vomits On-Stage (VIDEO)

Dierks Bentley sings about being drunk on a plane, but now the country superstar is also an expert on vomiting on a stage ... thanks to a drunk fan -- and the footage is disgustingly awesome!!

Dierks was performing at the Hershey Giant Center in Pennsylvania last night and brought two fans on stage to sing along to "Drunk On a Plane."

The truly gnarly part of this video is that ... we've all been right where this chick was -- just not in front of thousands of people. A rep for Dierks tells us he felt really bad for the fan.