Mariah Carey Awkwardly Pretends to Slap Dancer During MTV Video Music Awards

Mariah Carey's clearly not onstage a ton anymore ... 'cause her choreography was a bit awkward onstage at the MTV Video Music Awards -- including a fake slap she really didn't sell.

The singer-songwriter took the stage at UBS Arena in New York Sunday night to perform some of her hits and accept the Michael Jackson Video Vanguard Award -- a lifetime achievement presented at the ceremony each year.

After finishing up a song, a woman in an all-red outfit -- who Mariah called Bianca, a reference to a character from the 1999 "The Heartbreaker" music video -- came out ... and, Mariah pretended to smack her in the face -- all rehearsed choreogrphy.

Well, perhaps not rehearesed enough ... 'cause Mariah's fake slap was off-time -- and, looked pretty cringy. She seemed to heistate and got nowhere close to the dancer -- who did her best to sell the movement with a cartoonish flop to the floor.

Mariah kept right on performing ... and, she got a huge ovation when the show ended -- so, it seems no one minded the less than believeable smack.

Worth noting ... Mariah didn't do a ton of dancing during the show -- moving around the stage a bit gingerly and holding hands with dancers who seemed to be leading her around. She doesn't do a lot of live shows, so she might be a bit out or practice.

She sounded great though ... and, she thanked everyone when she accepted the lifetime trophy -- though she had to ask what took MTV so dang long!