Mike Tyson seemed to lose his cool on a plane on Wednesday night ... repeatedly punching a man in the face after the guy had apparently annoyed him.
TMZ Sports has learned ... the incident all went down at around 10:30 PM PT as Tyson was slated to fly out of San Francisco International Airport to Florida.
A witness on the plane says as he and his friend were boarding Tyson's flight ... the boxing legend was initially cool with them and the other passengers.
The witness tells us Mike took a selfie with him .