Robert Pattinson in Malibu Ca on April 6, 2012 Credit: AKM-GSI

Robert Pattinson may be a sex symbol to millions around the world, but the 25-year-old actor was "upset" after photos emerged of him paddleboarding wearing only swim trunks in Malibu March 30, an insider tells the new issue of Us Weekly (out now).

"He's really insecure about his shirt being off," a source says of the U.K. native, who painted-on sculpted abs for scenes in New Moon, the second film of the five-part Twilight saga.

Kristen Stewart's costar boyfriend is also stressed about his smoking habit, the source tells Us. "He's trying to cut back."

Pattinson's next film, Cosmopolis, hits theaters May 23. It also stars Jay Baruchel and Paul Giamatti.

Tell Us: Do you think Robert Pattinson has anything to be embarrassed about?