Shawn Mendes and James Corden Bid on Justin Bieber's Dirty Underwear During 'Carpool Karaoke'

Singing some of Shawn's classics and new music -- including "Treat You Better," "In My Blood" and "Mercy" -- the two also engaged in a stellar debate regarding the merits of buying a pair of Justin Bieber's dirty underwear. But that was not all as the two dove into Mendes' deep love for Harry Potter and practiced some solid road-rage techniques before hitting the ice for some hockey.

Shawn will be 20 by the end of the summer, and the "Stitches" singer just moved out of his parents' house. He told Corden he finally got his own place in Toronto, "which, at first, sucked because cooking for yourself and cleaning your house sucks until it's actually kinda nice." Corden called him out, saying there's no way he cleans his own house. Mendes bashfully admitted the comedian was right. "Yeah, I don't -- you're right. My mom still helps," he said, admitting that she still does his laundry as well.

The topic of laundry led Corden to informing Mendes that Justin Bieber actually avoids the whole washing-his-clothes thing entirely -- he simply wears a new pair of underwear every day! "I think he then sells them online," Corden joked, to which Mendes replied, "Genius." Shawn also admitted (under his breath) that he'd definitely buy Biebs' old drawers. "I'd probably cap it at like $500," Mendes said. Corden then asked Shawn how much he'd pay for a pair of his underpants. "I'd pay not to have a pair of your underpants," Shawn replied. "I would pay for them to be as far away from me as possible."

Shawn's a huge Harry Potter Fan and told Corden he even has a book at home in which he's written all the series' spells. On a scale from 1 to 10, Mendes admitted his obsession is at about a "9.5." So what is it about the books and films Shawn loves so much? "Just the magic. Like the wands and the little weird candies that make you turn into a lion and stuff," he said before admitting he doesn't think he'd ever outgrow his love for HP. Shawn also told Corden about the time he met the whole cast of the movies and said it was "one of the first times [he] was really, really starstruck."

Corden said he couldn't imagine Mendes getting angry and asked him if he ever gets road rage, to which the latter replied, "I don't even honk." Corden laughed, admitting that he lays his hand on the horn more times than he probably should, but when the receiving drivers' reactions, he clams up and pretends "they're not there," which Shawn says makes him "the worst type of guy." Corden then challenged Mendes to lower his window and shout, "Wrong lane, asshole!" He complied but said "it didn't feel very good."

When Corden asked Mendes what was "the most Canadian thing" about himself, the Toronto native said it was his love of ice hockey. Corden admitted he had never played before, so the two pulled over and tore up an ice hockey rink. "This is a mistake. I don't want to do this. This is a terrible idea," a heavily padded Corden said to Mendes before stepping onto the ice. "I've never been so uncomfortable!" The laugh attacks ensued as Corden made his way slowly and clumsily to the goalie post.