Former UFC champ Sean Strickland just proved yet again he's not one to play with ... flashing a gun on some pranksters who had just ding-dong ditched his home.

Strickland -- who last fought in the Octagon in January -- said the incident happened over the weekend ... at around 1 AM Saturday morning.

According to the fighter, some kids jumped out of a car near his pad, ran to the side of the house, and made a loud bang -- before bolting from the area.

In video captured by surveillance cams at the crib, you can see that just seconds after they left -- Strickland walked out with a bathrobe on ... and a firearm in his left hand.

Thankfully, no shots were fired ... and everyone made it away from the ill-advised practical joke unscathed.

"You guys have a car, it's Friday night," Strickland said in a caption on the footage. "Why aren't you out trying to get P? Kids these days. All the wrong priorities."

It's unclear if the guys knew it was Strickland's house ... but the 33-year-old said wild stuff has happened at his place before -- and he doesn't like to take chances with anything.

"Didn't see the doorbell alert till after...," he said. "Just so you all know! I get crazy stuff sent to my house.... lol!"