A woman threw a cup of urine over a bus driver after he told her to "have a nice day."
The woman was caught on CCTV peeing into a into a takeaway coffee cup at the back of the bus just moments before the bizarre assault.
She then got up and walked towards the door to get off.
As she did the driver politely told her to have a nice day, police said.
The woman asked the driver if he was talking to her, and when he replied 'yes', she took out a purple travel cup and threw its contents a him.
The woman was caught on CCTV peeing into a takeaway coffee cup just moments before the bizarre assault
She then got up and walked towards the door to get off
As she did the driver politely told her to have a nice day
"To say bizarre is really an understatement. It's a vulgar assault," Metro Transit Police Chief Ron Pavlik said.
CCTV showed the woman running away after tossing the liquid.
"Based on the video evidence we retrieved, the woman is seen at the rear of the bus relieving herself into a cup," Pavlik told NBC Washington .
The woman throws the urine at the driver
CCTV showed her running away after tossing the liquid
"I can't think of anything the operator did to warrant the assault."
The disgusting incident happened on the X2 bus at about 6.15pm local time on Saturday.
The driver was taken to a hospital and "decontaminated," police said.
One woman who regularly takes the X2 bus said she wasn't surprised by the attack.
"If it's the X2, it's a lot of crazy stuff on that bus. I've seen a man with a cup of spit on that bus before," she said. "He was sitting there spitting and spitting."