Philip Deazley, 21, said he and some friends were riding in a vehicle, playing with water guns in Portstewart, when squirted a police vehicle, which he said was not moving at the time, the Belfast Telegraph reported Tuesday.
Deazley said police pulled the vehicle over and he was temporarily detained.
"I think it's an absolute joke," Deazley said. "There were about 10 other people squirting with water pistols that night but I was the only one stopped. When the police stopped me they said I could pay an £85 [$130] fine for disorderly behavior but I wasn't paying that for squirting a wee bit of water. I'll go to court if it comes to that."
Police said a file has been sent to the Public Prosecution Service for possible charges in the case.
Deazley said no one was ever in danger from his water gun.
"It wasn't dangerous and the windows were fully up," he said of the police vehicle. "The other cars I squirted were stopped too and in a queue of traffic."