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(TMZ) - Justin Bieber was caught on camera peeing into a restaurant mop bucket... and laughing like he's the king of the world.

The clip was shot in NYC earlier this year -- sources tell TMZ Bieber and his friends were leaving some nightclub, exiting through a restaurant kitchen, and Bieber decided he needed to take a leak.

But rather than go to a bathroom like a normal person, Bieber whipped out his junk and whizzed into a yellow mop bucket used to clean the restaurant's floors ... meaning whoever's job it was to mop the place up had to physically change Bieber's pee water.

Watch the clip:

And the worst part... Bieber's friends act like the restaurant should be HONORED that the singer decided to urinate there. 

TMZ can't say for sure if the group was drunk, but it sure sounds like they were.

Oh yeah, at the end of the video, Bieber sprays a photo of Bill Clinton with cleaning liquid for some reason... saying, "F*** Bill Clinton!"

We don't know what Bill Clinton did to Justin Bieber...