It's summertime, and that means Jimmy Fallon and Justin Timberlake are back to crack themselves up in their recurring "The Tonight Show" camp sketch.

Jimmy and Justin returned to Camp Winnipesaukee last night, singing "What's Up" by 4 Non Blondes, and Gloria Estefan's "Rhythm Is Gonna Get You" -- since it's 1993 for them.

Keegan-Michael Key stole the show, breaking up the kids's fun as a new version of their irritated camp counselor.

Jimmy: "Hey, did Mr. Fletcher look different to you?"
Justin: "Yeah, way more theatrical."

That cracked them both up. Stay to at least the 7:45 mark for another celeb cameo, with Billy Crystal playing a 12-year-old camper who joins them for another song.

Watch the full 10-minute video. Yeah, it's long, and Crystal even makes a great joke about that:Check out the past Camp videos, and look forward to what 2018 brings these "best friends forever."

In addition to his camp cameo, Billy Crystal was a guest on the show last night, to talk Trump and share some advice for Fallon.

Want more stuff like this? Like us on Facebook.