The Dark Horse hit-maker dressed up as a clown for the video for her track Birthday and carried out a prank at a party, where she attacked a man with a piñata stick and staged a car accident, but the spoof incident left children in tears.
Eye witnesses told TMZ that Katy pranked a real birthday party and most of the guests had no idea it was a joke.
Children were crying and one woman "stormed away" visibly upset by her antics.
A teaser for the video: The hidden camera gag was shot at Knollwood Country Club outside Los Angeles and a video obtained by the website shows one little girl saying, "Mommy, I want to leave."
During an interview on Jimmy Kimmel Live, Katy spoke about going "undercover" at the bash, but didn't mention the fall out.
Speaking earlier this week, she said: "I just did a music video completely undercover as five of the world's worst birthday entertainers, because I was sick of making gorgeous music videos where I'm sexual."
Jimmy joked: "People are sick of that, yeah, really tired of looking at you." ( like seriously , who gets tired of looking at Katy, that person must have a disorder , even the Lion in her "Roar" video was spell bound )
The Kimmel interview:
Katy, 29, then previewed a clip of the video which sees her dressed as a clown drinking and burping, saying: "I'm not really a birthday party entertainer, I'm just trying to get some cash on the side,'' adding, ''Happy birthday kids."
Watch the TMZ footage here.