Recent encounter with someone who switched up their personalities

** not entirely sure if this is the right subreddit but im just interested in getting opinions on why this might have happened from a more psychological standpoint

So today I was on my way to the gym and I stumbled across a friend of mine, his friend comes along and I chat with my friend's friend (first time meeting him). It's all going smoothly and the convo is generally neutral, and I thought nothing of it. I was getting ready to go to the gym and leave the conversation so I just dapped him up (in a jokingly hard way, and then i kind of exerted pressure on his hand *I do this all the time as a joke because my grip strength is weak lmao + his hands were hella big so i knew he could crush my hand if he wanted to*) and he starts getting extremely offended, threatening to beat me up. I was caught by surprise because it seems like a relatively harmless thing, so in shock I leave to go where I was going but I just cant seem to understand how someone can act like this?

Might seem like a vent (partially is) but I am also interested in understanding why this might have happened so that I can avoid problems like this.

Some background is im not entirely extroverted but have been working on my social skills for the past 2 years (covid hit me hard so i was extremely introverted) so I might not have picked up on social cues or something?