Credit: Saleem Elatab-AhmadElatab/Splash News Online

While doing some post-Christmas shopping in NYC, Pete Wentz sported a black eye.

"The mean streets of NY got to him," his rep joked to

But a source close to the Fall Out Boy rocker, 30, tells Us he simply fell on the street and insists the bruise "is not as bad as it looks."

He and wife Ashlee Simpson - now playing Roxie Hart in the Broadway production of Chicago - seemed to have a more peaceful holiday, spending it with Simpson's family and their 1-year-old son, Bronx, in the Big Apple.

On Christmas Day, Wentz Twittered: "bought the lil kid sea monkeys today. if he can believe in santa, he can believe in sea monkeys."

His wife, 25, also was in the festive mood, Twittering: "merry merry christmas everyone..ahh I love christmas."