For 364 days of the year, D.C. is about as funny as daytime C-SPAN. But for just one night, the White House and the journalists who cover it put aside their differences, put on their tuxes and gowns, and come together for the White House Correspondent’s Dinner. Celebrities, journalists, and politicians gathered Saturday night for the annual dinner sometimes known as “nerd prom” — an event so popular there’s even a documentary Washington’s biggest night. It’s a chance for the president to relax and crack a few jokes of his own.