Texas Triplets Turn Yearbook Photos Into Knock-Knock Joke

And they are outta there.

Northwest High School seniors Kassidy, Keaton, and Kylee Durham of Fort Worth, Texas, took the opportunity — granted to them by nature — to leave a lasting mark on their alma mater with a very clever yearbook joke that went viral after being posted to Twitter by a classmate.

"I think it was more of a surprise to us, from how many people mentioned it on Twitter and how fast it blew up," Kassidy told ABC News.

Rather than use the "senior quote" space under their senior pictures for a teenage platitude, the triplets instead created a wry farewell with a knock-knock joke.

Under Kassidy's photo, it read "Knock knock." "Who's there?" came the reply beneath Durham brother Keaton's, followed by the punchline under Kylee's picture to seal the deal, "Not the triplets. We graduated."

ABC reports that the triplets graduate on June 7 and that all three plan on attending the University of North Texas.

(H/T: Dowzerw)