"I had no time to realize what was happening," 22-year-old Pernilla Nordqvist told the Expressen newspaper following the incident, which took place in the early hours of Sunday morning.
"I flew. Only the head and legs were still in the car, quite a bit of the upper body and legs were also sticking out."
Nordqvist was just a few blocks from home as she pedalled through the otherwise quiet streets of Skellefteå in northern Sweden after having been out with friends.
"I was cycling down a bicycle path near the street when I saw the car coming toward me," she told the local norren.se news website.
At first Nordqvist thought the car would turn to avoid hitting her, but the next thing she knew, the passenger's protruding posterior sent her hurdling to the ground.
A passerby who witnessed the malicious mooning promptly called police, who were also at a loss for how to describe the unusual accident.
"I'm not sure how I should put this since I've never seen anything like it," Joakim Oja of the Skellefteå police told the paper.
"The butt of a passenger was hanging out the window of the car and that's what hit the cyclist."
After the mooning passenger nearly left her seeing stars, Norqvist was forced to see a doctor following the violent rear end collision.
"I had pain in my neck and legs and the doctor prescribed pain pills," she said, adding that the lingering pain prompted her to take a day off work.
Oja said police had identified the owner of the offending rump and the other passengers in the car. While no criminal charges have been formally filed, police are treating the incident as a case of reckless driving.