A cop who thought she was a big wheel got a lesson in law from this high-school kid.

The NYPD officer slapped Brooklyn high-schooler Isaih Rosemond with a summons for riding his “bike’’ on the sidewalk — even though he was on a unicycle and correctly told the cop it wasn’t against the law to ride the one-wheeler there.

When a patrol car first honked and pulled up behind him, “I had a smile on my face,” recalled Rosemond, 18, who was on his way to school when he was stopped on Rockaway Parkway in Canarsie at around 8 a.m. May 23.

“I took off my headphones and walked up to them. A lot of people stop me because they are intrigued about unicycles. So I just assumed they were going to ask me about my unicycle,’’ the teen told The Post yesterday.

But Rosemond said he quickly realized that the cop who got out of the car wasn’t amused.

“Don’t you know it’s illegal to ride a bike on a sidewalk?’’ barked the officer, identified as Nicole Ortiz from the badge number Rosemond provided from the summons.

The teen — anxious to hop back onto his $200, black-seated Torker unicycle to get to school on time — tried to protest.

Rosemond even whipped out his iPhone and quickly looked up an official government Web site that detailed the legal code to prove that unicycles are not banned from sidewalks. “I told her . . . She just brushed me off,’’ he said.

The officer then proceeded to write him a ticket for “biking on sidewalk,’’ which carries a maximum fine of $100.

“I think she was trying to meet a quota in giving out tickets,’’ he said.

“I live in Canarsie. There are so many people doing drugs there,’’ added Rosemond, whose neighborhood is covered by a police precinct where robberies, sex attacks and assaults have soared in recent months.

“Why pull me over? It’s not fair. She should have known the law. She’s a cop.’’

According to the city Department of Transportation’s rule banning bikes on sidewalks, “A bicycle is defined as [a] two- or three- wheeled device.’’

Rosemond said that as he tried to argue his point, he looked up the case of a circus performer who successfully fought two summonses he was given for riding a unicycle on the sidewalk. He said the officer’s amused male partner just sat in the car the whole time.

The teen said that when he finally made it to Edward R. Murrow HS in Midwood 25 minutes late for his first class, his teachers were understanding.

“They know I’m not a bad kid,’’ he said.

Rosemond said he took up the unicycle in February. Also a pianist and guitar player, he said he now rides his cycle more than four miles a day to school, about an hour from his home.

The teen graduates at the end of the month and will attend Manhattan Community College in the fall. He wants to go into the medical field.

As for his August court appearance, he said, “I’m confident I’ll win.’’

An NYPD rep insisted that the ticket was written for reckless riding on the sidewalk, despite what the officer wrote on the summons.

Additional reporting by Rebecca Harshbarger and Doug Auer