The 'Mean Girls' star's dirty antic was busted after staff members heard moaning noises coming from inside a cubicle, and discovered Lohan being naughty with the male patient.
"Staff were alerted to the bathroom because there were strange noises coming from inside and two voices could be heard. When they opened the door, Lindsay was in a compromising position with the guy — who's also at Cirque for drug rehab," the News of the World quoted an insider, as saying.
"Rumours spread like wildfire across the place that they'd been having sex.
When staff found them they were all flustered and Lindsay's hair was all over the shop," the insider added.
The insider went on to say that Lindsay fought back because she was in a bad mood about being given toilet-cleaning duties.
"She was livid that she was given the miserable task of cleaning the bogs so the theory was she'd do something really dirty in there. Lindsay has been throwing tantrums like a little kid, telling everyone that she misses partying," the insider said.
"It's a lost cause as it's clear that she can't wait to get back to her normal, partying lifestyle," the insider added.