JUSTIN BIEBER TO FEMALE FAN Look at You ... YOU MAKE ME SICK

Justin Bieber was grossed out by a female fan getting all up in his space for a pic, and he let her know it ... straight up. 

Justin was in Melbourne, Australia Saturday, where a young girl tried snapping a selfie of herself next to the pop star as he grubbed on some finger food. He lectures her on respect ... and then burns her with a harsh line.

Bieber ... don't bother him ... he's eating.