Smile! Cameron Diaz and Jimmy Fallon photobomb tourists

Tourists visiting New York City’s Top of the Rock Observation Deck got a special surprise with their snapshots this week: a brush with celebrity photobombers Cameron Diaz and Jimmy Fallon.

In a clip from Wednesday’s “Tonight Show,” Fallon explains that his crew told sightseers they were being photographed for the building’s website. The tourists then are seen smiling for the camera as Fallon and “The Other Woman” star — both disguised in dark hoodies — sneak in from the back and strike goofy poses.

Behind one group, Diaz freezes with a wide grin on her face, hair whipping in the wind. In another shot, a woman and three girls smile sweetly as Fallon and Diaz leap in the background with arms extended, as if in an old Toyota commercial.

The antics only get zanier from there. Diaz and Fallon tiptoe behind an unknowing couple and perform clumsy crane kicks (no apologies to “Karate Kid”), then go on to don Pharrell-style hats, bust out their best Charlie’s Angels moves (not a stretch for Diaz), and in a meta moment, pose for a selfie as a family of four grins unknowingly in the foreground. As he did with “Mad Men” star Jon Hamm back in March, Fallon photobombs a shot as he and Diaz split a massive sandwich, with the stars gnawing at either end. (If Fallon keeps this up, the Big Apple might soon be known as the Big Hoagie.)

When the tourists finally realize what’s happening, reactions run the gamut. One young woman whips around, shrieks, and gapes at Fallon in a starstruck stupor. One unflappable mom barely bats an eye as she embraces Fallon like a stray son-in-law.

Apparently once you photobomb, you’re family.

“The Tonight Show” airs weeknights at 11:35 p.m. on NBC.