Yes, I agree that tu or vous are not marks of politeness but marks of social distance / deference.

That's the reason why French people, regardless of whether they are polite or not, usually do not have to guess what to use. They know if the person in front of them is close enough or not and they remember if using tu was agreed in case the vouvoiement would have been the default usage.

What might confuse English people is when they are told using tu to someone you should have say vous is impolite, and using vous to someone you should have say tu is excessively polite.

They shouldn't worry that much. This tu/vous ruleset is very relaxed when applying to non native speakers learning French. We are very lenient in that case just like we do not care about young children who say tu to everyone. They simply haven't already learn to use the singular vous.

Switching from vous to tu is done either never or once, commonly after an invitation to do so from one of the parties.

Switching from tu to vous is extremely rare. Once you start saying tu to someone who doesn't express disagreement, there is no reason to revert.

Your fight example is a case where this can happen but it is still a very uncommon kind of event. The switch is indeed done to put some distance again between the people involved.

Another case is people talking together at the TV or radio who switch to vous for consistency and deference. A journalist that say tu in private with an some interviewee and vous with some others will use vous with all of them in public.

See also How do you decide whether to use "vous" or "tu"? / Comment choisir entre « vous » et « tu » ?

Yes, I agree that tu or vous are not marks of politeness but marks of social distance / deference.

That's the reason why French people, regardless of whether they are polite or not, usually do not have to guess what to use. They know if the person in front of them is close enough or not and they remember if using tu was agreed in case the vouvoiement would have been the default usage.

What might confuse English people is when they are told using tu to someone you should have say vous is impolite, and using vous to someone you should have say tu is excessively polite.

They shouldn't worry that much. This tu/vous ruleset is very relaxed when applying to non native speakers learning French. We are very lenient in that case just like we do not care about young children who say tu to everyone. They simply haven't already learn to use the singular vous.

Switching from vous to tu is done either never or once, commonly after an invitation to do so from one of the parties.

Switching from tu to vous is extremely rare. Once you start saying tu to someone who doesn't express disagreement, there is no reason to revert.

Your fight example is a case where this can happen but it is still a very uncommon kind of event. The switch is indeed done to put some distance again between the people involved.

Another case is people talking together at the TV or radio who switch to vous for consistency and deference. For example a journalist that say tu in private to an interviewee and vous with some others will use vous with all of them in public.

See also How do you decide whether to use "vous" or "tu"? / Comment choisir entre « vous » et « tu » ?

Yes, I agree that tu or vous are not marks of politeness but marks of social distance / deference.

That's the reason why French people, regardless of whether they are polite or not, do not have to guess what to use. They know if the person in front of them is close enough or not and they remember if using tu was agreed in case the vouvoiement would have been the default usage.

What might confuse English people is when they are told using tu to someone you should have say vous is impolite, and using vous to someone you should have say tu is excessively polite.

They shouldn't worry that much. This tu/vous ruleset is very relaxed when applying to non native speakers learning French. We are very lenient in that case just like we do not care about young children who say tu to everyone. They simply haven't already learn to use the singular vous.

Switching from vous to tu is done either never or once, commonly after an invitation to do so from one of the parties.

Switching from tu to vous is extremely rare. Once you start saying tu to someone who doesn't express disagreement, there is no reason to revert.

Your fight example is a case where this can happen but it is still a very uncommon kind of event. The switch is indeed done to put some distance again between the people involved.

See also How do you decide whether to use "vous" or "tu"? / Comment choisir entre « vous » et « tu » ?

Yes, I agree that tu or vous are not marks of politeness but marks of social distance / deference.

That's the reason why French people, regardless of whether they are polite or not, usually do not have to guess what to use. They know if the person in front of them is close enough or not and they remember if using tu was agreed in case the vouvoiement would have been the default usage.

What might confuse English people is when they are told using tu to someone you should have say vous is impolite, and using vous to someone you should have say tu is excessively polite.

They shouldn't worry that much. This tu/vous ruleset is very relaxed when applying to non native speakers learning French. We are very lenient in that case just like we do not care about young children who say tu to everyone. They simply haven't already learn to use the singular vous.

Switching from vous to tu is done either never or once, commonly after an invitation to do so from one of the parties.

Switching from tu to vous is extremely rare. Once you start saying tu to someone who doesn't express disagreement, there is no reason to revert.

Your fight example is a case where this can happen but it is still a very uncommon kind of event. The switch is indeed done to put some distance again between the people involved.

Another case is people talking together at the TV or radio who switch to vous for consistency and deference. A journalist that say tu in private with an some interviewee and vous with some others will use vous with all of them in public.

See also How do you decide whether to use "vous" or "tu"? / Comment choisir entre « vous » et « tu » ?