PopUps: Bieber Poses for Men's Health, Faces Worst Nightmare in Roast Promo

After getting down to his Calvins earlier this year, pop heartthrob Justin Bieber is showing off his bod as he graces the cover of the latest issue of Men's Health.

Bieber, who recently turned 21 (horray...), bares his tattooed body for the April edition of the fitness magazine, flexing in a number of black-and-white sexy images.

According to Rap Up, the "Confidant" singer has been something of a gym rat recently, working on his body as his workout plan consists of lifting weights five times a week. He also says he's working on his reputation (remember his strange Facebook apology?)

"This has been a really big year for me, as far as figuring stuff out," the Biebs told Men's Health. "A year from yesterday, I was in jail."

The singer also gives some random facts about himself, like that he can solve a Rubik's Cube "in less than a minute" (lol) and his favorite part on a woman is her legs.

"I really like jean shorts and like a tank top. Or spandex," he told the magazine.

He also compared himself to Michael Jackson (lolol), saying, "I'm a perfectionist, too. I've always been different, and I haven't been afraid to be different."

Check out Bieber's cover below and the rest of steamy photos in Men's Health via Rap Up.

In other shirtless Bieber news, a new promo for his March 30 Comedy Central roast made its way online this week. The one-minute 13-second clip, parodies Bieber's now-infamous Calvin Klein underwear ad with roast host Jeffrey Ross in a wig to play model Lara Stone, who was featured in the ads with Bieber.

"Hey man. I'm your worst nightmare," Ross tells Bieber. "Are you ready?"

"No," the singer replies.

Ross then says: "I want to stick my pinky in your asshole."

Let's expect lots of gay jokes during the roast.

Watch the clip below:

This story is part of our special report: "PopUps". Want to read more? Here's the full list.