Jack Doherty is spilling on his Miami arrest … telling TMZ the whole thing was so mind-numbingly boring, he’s actually calling it the worst day of his life.

The embattled influencer tells TMZ it was a brutal slog — first stuck in a tiny cell with a cop for five hours, then shuffled off for a mugshot and fingerprints … before spending another 10 hours in a big holding room where he could finally make some calls.

The day didn’t even end there … the 22-year-old says he got thrown into yet another cell, took a nap, and then got jolted awake by guards who, he claims, were super nice — even telling him TMZ had already posted his mugshot — before letting him finally go.

Looks like he might’ve gotten the memo … ’cause he says he plans to be good and stay outta jail from here on out. But he’s also making it clear that doesn’t mean seeking drug treatment — even though he was popped for amphetamine and marijuana.

Still, despite all the boredom and regret, he says the whole arrest was stupid … a vibe he doubled down on later, bragging he posted his own $3,500 bail the second he got the chance.