Long story short: Milbank, the dependably entertaining, always informative columnist for the Washington Post, was at a party hosted the Post's Pulitzer Prize-winning editorial cartoonist Tom Toles and his wife. At some point Milbank raided Toles’ bedroom, put a pair of Toles’ underwear on over his pants, wore it around the party.
Not exactly doing nude cannonballs into the pool or setting a sofa on fire. But, it’s Washington. You take what you can get. Given the crowds at these things, this is probably preferable to the nude cannonballs.
(Sorry the pic doesn’t show Milbank’s face – you’re going to have to trust us that he was the only person at the party wearing underwear over his pants.)