Rihanna Embarrassed By Mother's Ashton Kutcher Joke (VIDEO)

Rihanna isn't someone we'd call shy -- whether composing raunchy tweets or wearing barely-there clothes, she doesn't appear to blush easily. Still, the 24-year-old pop star's mother, Monica Braithwaite, knows how to push her daughter's buttons.

According to the New York Post, Rihanna wasn't too impressed when her mom joked about the singer's alleged romance with Ashton Kutcher, at Tuesday night's TIME 100 Gala at Lincoln Center in New York. Rihanna brought her mom to the gala where she was being honored for making the magazine's annual list of the 100 most influential people.

The exact joke Rihanna's mom made hasn't been reported, but it was enough that Rihanna tweeted about it after the event:

Rumors that Rihanna and Ashton were an item began after the singer was spotted leaving the actor's house on March 22. Her 4 a.m. exit from Kutcher's swank Los Angeles mansion had everyone wondering what was up between the two.

But the rumored romance with Kutcher just isn't something the singer wants to talk about, and she even told off one intrepid reporter who dared ask about the alleged relationship.

Rihanna maintains she's single, but she recently tweeted that she went on her first date in two years. Just who was her lucky date? That would be Melissa Forde, who has long been rumored to be more than just a friend to the singer.