The "Gossip Girl" star talks to Men's Health about love -- and jeans -- in the magazine's November issue and "Denim Guide: 2009."
Speaking about his co-star and real-life love Blake Lively, Penn says, "Having a relationship with someone you work with might not always be the smartest move," he says.
"But it's been wonderful to be in a relationship where we can both identify with what the other is experiencing."
On his personal style, he adds: "There's a stigma about looking like you're tying too hard, but that doesn't mean you shouldn't try at all. I really think that's a bigger mistake."
The new issue of Men's Health is on stands today.