You’re 5-foot-7 and 173 pounds and you’ve had this crazy NFL dream from the time you were 3 years old, and now the doubters and the naysayers who have followed you every step of the way are reminding you that you are the littlest Jet, and an undrafted free agent no less, confronting gargantuan odds.

So here is Greg Dortch, backup slot receiver and punt returner, carrying the banner for all little underdogs everywhere who dare to dream the biggest possible dream.

The tweet, from @_GDortch, was posted on Monday night:

“They Tried To Lock Me Out … I Kicked The Door Down.”

Greg Dortch hasn’t kicked the door down to the 53-man roster just yet. He will try to kick it down in Thursday night’s preseason finale against the Eagles.

The way Bruce Harper kicked it down in the summer of 1977.

Harper was Dortch back then, a 5-8, 175-pound running back out of Kutztown (Pa.) State, when he walked into the Tower E dormitory that housed Jets players on the Hofstra campus.

“The first day I was there, I remember coming into the dorm, and Greg Buttle poured a bucket of water on me,” Harper recalled. “He was up on the second floor. And I looked up and I saw people laughing. And I said, ‘OK, I guess this is initiation.’

“And then I remember I got in the elevator, and all these big guys were there and they were laughing at me and saying, ‘What position are you gonna play, offensive guard?’ or something, you know. It was trying initially, but that was to be expected.”

The Jets were Harper’s only chance, only after he had asked teammate Walt Michaels Jr., son of then-head coach Walt Michaels, to lobby on his behalf.

“I went over to the Giants first, and Coach [John McVay] was sitting there having lunch, and he looked up and said hello, and then he went back eating his food,” Harper said.

Cut down to sighs again.

Harper’s NFL dream began in the living room of his Englewood, N.J., home, then at Benning Park, then at Dwight Morrow High School. Harper laughs at the memory of his Uncle Earl telling him he was too small to play in high school.

“He said I was gonna get my head knocked off,” Harper said.

Harper refused to listen every step of the way.

“I just wanted to play football,” he said. “I didn’t know anybody from Penn State or anybody from Purdue or the No. 1 draft choice or anything. It made no difference to me. I wasn’t afraid of anybody.”

He had never returned kicks. Didn’t matter. Bruce Harper, No. 42, would be a Jet for eight seasons. He remembers catching a screen pass in the right flat from Richard Todd for a 45-yard touchdown at Shea Stadium against Earl Campbell’s Houston Oilers.

“It was so funny, I’m laughing right now, all the guys come over and they just picked me up like we won the Super Bowl it something,” Harper said.

Harper would get 60 minutes from a Super Bowl when the same screen was called for him in the infamous AFC Championship Mud Bowl. Except A.J. Duhe, who accounted for three of Todd’s five interceptions, turned this one into a pick-six. Harper could only watch helplessly as Duhe rumbled to the end zone. “So heartbreaking,” Harper said.

He would rush for 1,829 yards. He would catch 220 passes for 2,409 yards. He would return 243 kickoffs for a 22.3-yard average. He would return 183 punts for a 9.7 average with a touchdown. He was a fan favorite.

“I didn’t realize I was a fan favorite,” Harper said. “I was just out there playing my heart out, having fun, man, and just doing my thing.”

Dortch has displayed the same huge heart and quickness and elusiveness.

“You cannot tell him that he can’t do something,” Greg Dortch Sr. told The Post. “He hates to lose.”

Kevin Higgins, associate head coach, recruiting coordinator and receivers coach at Wake Forest, recalls Dortch making good on a vow to play a week after suffering a high ankle sprain.

“He wills things to happen,” Higgins told The Post. “That’s what he’s had to do his whole life.”

Where there’s a will there’s a Bruce Harper way.

“My thinking is if you think you are too small to play in the NFL,” Harper said, “then you are too small to play in the NFL. Why not me? That was my attitude.

“Tell me why not me?”