San Mateo County sheriff

Celebrating your birthday? Don’t kick off a strange crime spree by pretending to be a cop and pulling people over and harassing an underage girl.

Allen Grabovetsky never got that memo and did all those things on his birthday, then sent threatening text messages in the weeks afterward, San Mateo County authorities say.

It all started on Dec. 6, the day Grabovetsky, a San Mateo resident, turned 19, said District Attorney Steve Wagstaffe.

A woman was driving a Panera Bread van for work when Grabovetsky pulled her over in Millbrae while driving his parents’ teal pickup truck, outfitted with a siren and flashing red lights, the prosecutor said.

Grabovetsky told the woman that she was speeding “and asked for money to let her go,” the prosecutor said. The woman, suspecting it wasn’t a real cop who had stopped her, asked for the ticket. Grabovetsky “let her go with a warning but demanded she call him ‘officer,’ ” Wagstaffe said.

A few minutes later, Grabovetsky tried to pull over a car with an airline pilot and flight attendant on Highway 101 as they were on their way to San Francisco International Airport, Wagstaffe said. The two also didn’t believe he was a real cop and got the license plate number of his truck and called police.

Grabovetsky allegedly pulled over two more drivers, one on Highway 1 and the other in a theater parking lot in Redwood City, Wagstaffe said. Neither one of them fell for it, either.

Finally, a Redwood City police officer — a real one — found Grabovetsky driving in the area and cited him.

That same day, Grabovetsky allegedly approached a 15-year-old girl sitting on a bench with friends outside the Hillsdale Mall in San Mateo. He knelt, put his hands on her knees and asked how old she was, Wagstaffe said. When she said 15, he allegedly replied, “It’s OK with me.”

The girl walked away, but Grabovetsky followed her, touched her on her back and said, “Come on, baby, we can go back to my truck,” Wagstaffe said.

Four days later, Grabovetsky allegedly tried to sell marijuana to someone on the Hillsdale train platform. He told officers who arrested him that he was in the military and that they should let him go, Wagstaffe said.

Then, on Dec. 16, an 18-year-old friend of Grabovetsky’s began getting threatening text messages from him, including ones that read, “I’m going to literally put a knife through your head,” “I’m going to murder you” and “I’m going to show up and kill your parents,” authorities said.

Grabovetsky faces a long list of charges, including impersonating a police officer, stalking, annoying a child and battery. He is being held at San Mateo County Jail in lieu of $120,000 bail.