RIHANNA went after a fan with her MICROPHONE after they got too grabby at a concert in Birmingham, England on Monday! 

In a video that's popped up online, Rihanna is down in front of the stage, handing out high-fives while she sings "We Found Love".  Then you can see someone yank on her shirtsleeve, and she swings the mic at them.  It's not clear if the person who grabbed her was a man or a woman.