A Florida cop's outta work after a wild incident -- his own body cam captured him slamming his patrol car into a civilian's vehicle ... while he was distracted by porn on his phone.

The video shows Lake County Sheriff's Deputy Tristan Macomber slamming into another vehicle, his airbag deploying on impact -- moments later, he’s outside the car, picking up the phone from the floor and casually tossing it onto the seat, then checking on the other driver.

An internal affairs report from 2 weeks after the November crash claimed Macomber initially blamed the wreck on his brakes locking up when the car ahead stopped for a school bus.

Turns out, it was Macomber's eyes -- not his brakes -- that were locked on some XXX-rated visuals. Investigators reviewed his vehicle's dash cam and caught him clearly distracted, holding a cell phone in the seconds leading up to the crash.

When questioned initially, Macomber claimed he was scrolling through text messages in a group chat with other deputies at the time of impact. But later, he fessed up -- admitting he was actually viewing pornographic material on his personal phone.

Macomber racked up 3 policy violations -- lying about the incident, using an electronic device for prohibited content, and evidence showing he wasn't wearing a seatbelt during the crash.

NSFW at any speed!!!