Do you mean work settings? I think traditionally Sex has been a staple of social settings; it's why a non-trival amount of people play novice sports (to meet future spouses).
Sex, Politics, Religion were the traditional ones to avoid. I'd also add 'childcare/how to raise children' as another one that can easily escalate/some people have very strong opinions on.
It's like all those bar leagues where people play softball for 90mins and then hang out at the bar afterwards for the rest of the day.