My 2-year-old son has decided to become a nudist.

Turn your back on him for 90 seconds and he disrobes — shoes, socks, pants, shirt, diaper, everything comes off. After he strips, he puts his clothes in a neat pile and runs.

Adding insult to injury, when you chase him he says: “Too slow. Too slow.”

My sister — who visits us from Nashville about once a month and loves to play jokes — has taught the boy to sing: “Whoop, there it is!” Now, I have a baby who runs through the house nude while singing “Whoop, there it is!”

Nice.

My wife was out of town last week, and the third time the baby undressed himself I lost my cool.

“Son, you’ve GOT to keep your clothes on!” I said. “Seriously.”

“It was an accident, Daddy,” he said, his head tilted backward to look straight up at me. Spittle was flying out of his mouth like Daffy Duck as he struggled to pronounce the word AC-CI-DENT.

“No, it was not an accident,” I said, looking down. “Your clothes do not jump off your body by accident.”

“Yes, it WAS an accident, Daddy,” he insisted. “Yes, it WAS.”

I’m terrified that he will pull this stunt at school, and I will have to squirm and answer questions from an early-childhood educator.

“Mr. Kennedy, can you please explain your son’s odd behavior?”

“Well, yes, I can,” I will say. “I can honestly say that whatever he did was an accident. If you don’t believe me, just ask him.”

Sometimes, getting my toddler’s clothes back on him is like trying to put pantyhose on a frog. We’ve even tried double-teaming him. My 7-year-old son held down his little brother’s arms while I tried to thread his churning legs into a Huggies Pull-Up.

“Diaper upside down!,” the baby wailed, landing several kicks to my chin and stomach in the process.

“No, your diaper is not upside down,” I said.

“Yes, it IS upside down,” he insisted, still kicking. “Yes, it IS.”

Actually, the idea of upside-down clothes is not outside the realm of his experiences.

His preschool teacher has taught him to put his jacket on the floor, bend over, insert his arms, and fling the coat back over his head. When everything works right, it is the cutest thing ever. When it doesn’t work — about 75 percent of the time — he gets tangled in the coat. It covers his face and traps his arms over his head.

“Coat too tight,” he said one time, staggering forward and bumping into a wall.

“That’s one way of looking at it,” I said, rescuing him from his straightjacket.

While his mother was away this week, I let him sleep in the “big bed” with Daddy. He must dream of being a professional wrestler because he kicks and jabs me all night long.

He also managed, every single night, to shift his body 180 degrees so that he woke up with his head at the foot of the bed. I think this child has some sort of strange “upside-down” condition. I’m thinking about tattooing the words “this side up” on his forehead.

When he was two days old, a doctor told my wife and I that our newborn son seemed, well, a little “quirky.” This, I’ve decided, might have been the most astute observation in the history of American pediatric medicine.