Apparently, the First Lady was speaking in front of 200 people at a private DNC fundraiser someplace on Tuesday evening, when a LGBT heckler shouted something:
"One of the things I don't do well is this," Obama said, per the pool report. She left the podium and moved toward the protestor, saying they could "listen to me or you can take the mic, but I'm leaving. You all decide. You have one choice."
Ironically, the heckler later complained about Mrs. Obama's lack of civility.
Anyway, don't mess with Michelle.
Update: BuzzFeed has posted audio of the confrontation: