Insane moment for ex-UFC fighter Dean Lister ... who pulled a firearm on a man who was robbing his house -- and the whole thing was captured on video.
42-year-old Lister -- who was 13-7 as an MMA fighter -- says he arrived to his San Diego home around 8 PM on Saturday when he saw a tatted up bald dude inside of his kitchen.
The man was super sketchy and told Lister he thought the home was a church -- but when Lister continued to press, the man picked up a hammer in a very threatening manner.