Caillat, 29, surprised the audience at the pop-up replica of Central Perk, when she sang the track, originally sung by actress Lisa Kudrow on the TV show, reported E! Online.
"Smelly cat, smelly cat what are they feeding you? Smelly cat, smelly cat it's not your fault," she sang.
"That was cool! Singin at the CentralPerk. My favourite show ever 'Friends'," Caillat tweeted after her visit.
Last month, the show celebrated its 20th anniversary.