Comedian Joan Rivers is being criticized for joking that First Lady Michelle Obama is transgender, which makes Barack Obama the nation's first gay president.

Rivers, 81, reportedly made the joke earlier this week after performing an impromptu wedding ceremony for a gay couple in New York City.

(Related: Joan Rivers performs surprise wedding for gay couple.)

In a brief on-the-street exchange with an unidentified reporter, Rivers said she was “excited” about the wedding.

“And I think I should do very well because I don't charge,” she quipped.

“And do you think that the United States will see the first gay president or the first woman president?”

“We already have it with Obama, so let's just calm down,” she joked. “You know Michelle is a tranny.”

“I'm sorry, she's a what?” the reporter asked.

“A transgender,” Rivers answered. “We all know. It's okay.”

It should be noted that “tranny” is considered a slur.