(+vs, +Martial Arts, +Story) Gangsters or organized crime groups. Are they truly at a level that ordinary people should never mess with?;;;

The common saying is
“Gangsters, thugs, gangs, or the mafia—if you run into an actual athlete or medalist, you might as well consider yourself dead.” That is the general consensus, right?
However, that applies specifically to professional athletes. Does that mean if an ordinary person who doesn't exercise at all and has no physical strength messes with them, they will actually be beaten to death?..
An acquaintance of mine once went to a nightclub and got rejected, so they just left.
When I asked, “Why didn't you just fight back?” they replied, “Do you think the guys praying or standing guard at the club are joking around?”
Even this person was a practitioner of boxing, kickboxing, and Muay Thai.