Lady Gaga Refused to Sing Onstage with Madonna?

At her St. Paul stop on her MDNA tour, Madonna had a few words to say about Lady Gaga.  She praised her audience for being the best fans and then said "So take that, Lady Gaga."  She then continued saying, "You know, I invited her onstage to sing with me. But, she turned me down. It's okay. I've been rejected before. It builds a little character."

SOURCE

Here's the video. Celebrities really can't get away with anything these days with Youtube.   Not too long ago, Madonna was booed after she shared that she would be voting for Obama in New Orleans.

Start at the :37 second mark