Machine Gun Kelly Spits Vodka into Fan's Mouth

More like Shotgun Kelly ... 22-year-old rapper MGK threw back a giant shot of vodka during a concert in L.A. this weekend -- then SPAT IT INTO SOME CHICK'S MOUTH ... and TMZ has the bizarre footage.

The rapper was performing at the Rock the Bells festival in San Bernardino Sunday -- when he took a massive swig out of a vodka bottle, then walked into the crowd with the liquid still in his mouth.

Once he found his lady target -- using boob-dar -- MGK mother-birded the booze into the girl's anxiously-awaiting maw. It's pretty disgusting.

Thankfully, the girl loved it.

A rep for Rock the Bells tells TMZ ... MGK was kicked out of the event following the performance ... but it wasn't because of the vodka swig ... it was due to an "action that happened backstage."