Credit: Jon Kopaloff/FilmMagic

Justin Timberlake has only one regret in his career: sporting over-the-top costumes and seriously cheesy hair during his 'N Sync days.

"There were many moments in my teenage years where I succumbed to, um, the weirdness of the group I was in," he tells the May issue of Details. "And in trying to conform -- we're marionettes! -- I ended up looking like a moron."

These days, the singer-turned-actor, 31, takes a manlier approach to grooming. "I don't like when I see guys do too much hair gel. I don't mean Pauly D -- because that's basically performance art. But when you use enough hair gel that your hair becomes a sculpture—and you wanted it to look that way? It's just weird."

Jessica Biel's fiance prefers to rock a "shaved head" instead of the platinum blonde curls he once sported. "It's scary the first time you do it, because you don't know what's under there -- you could have some weird knot -- but a shaved head is just so easy."

The Friends With Benefits actor -- who moisturizes with Kiehl's Facial Fuel -- tells Details every man should go to "an actual barbershop" with "the whole hot-towel, old-school experience."

"You sit there and get your hands massaged while getting a shave? Nothing wrong with that."