Christina Aguilera's Carpool Karaoke sees Melissa McCarthy show off her rapping skills

We've had Madonna, we've had Britney Spears. Jennifer Lopez, Pink, Katy Perry, Gwen Stefani, Lady Gaga, we've had all of them too. And now it's Christina Aguilera's turn to take her timeless pop hits around the streets in Carpool Karaoke. The singer and The Voice coach sang 'Fighter', 'Genie in a …