Credit: James Devaney/

Not-so-serious ScarJo!

Scarlett Johansson lets loose in some unlikely places, even 1600 Pennsylvania Avenue! In an appearance on Anderson Cooper's eponymous talk show, the 27-year-old actress opened up about why she loves the White House Correspondents Dinner.

"They call it the prom -- Washington's prom," she said. "For me, I feel kind of like a chaperone. [I just] enjoy it and don't have to be completely involved."

"We're just expected [as entertainers] to get drunk and make fools of ourselves," she quipped. "The Republican senator's the one that's supposed to be like on the straight and narrow."

Cooper, however, doesn't share Johansson's enthusiasm for the event. "They're people I have to interview at night on CNN, so I don't want to interact with these people," he admitted.

At the White House dinner this spring, a witness told Us Weekly Johansson and then-beau Sean Penn made out "right as the main course of the dinner was being put on the table." Johansson even sat in Penn's lap during part of the meal.