What people aren't considering is how and why the parent or pupil results in using swearing.
I'm not advocating swearing but I'm empathetic to how situations arise.
You are a pupil. It's zero tolerance. You realise before you attend lesson A you've not got your homework. Your anxiety increases because you know it's zero tolerance.
The zero tolerance leaves you feeling powerless. The whole ethos of zero tolerance is that teacher is all powerful and student loses their voice - and realistically their humanity. Humans make mistakes and have outside influences in their lives.
You attend lesson and are instantly put in detention for not having the homework. No questions asked. Therefore no empathy to your situation. At some point all that power from above stripping you of a voice will cause you to explode. Rightly or wrongly you may swear.
But stripping students of a voice is treating them with a lack of respect. Respect should be one of the biggest values in a school and should work both ways.
I remember the closest I became to swearing on a phone to a teacher. She actually told me my ds was 50% responsible for all disruption in class - yet could give me no concrete examples of his behaviour. Her reasons for this were - his writing is illegible, he is socially immature, he cannot work in groups effectively and he is easily distracted.
I did not and do not disagree that these behaviours are evident in ds. In fact all are recorded on his EHCP with support to meet outcomes related to them.
The teacher also couldn't explain to me why my ds writing being illegible made him 50% responsible for the pupils who decided to talk over her, not having the right equipment and searching for it when she wants them to settle down to work etc.
I'm a great believer at looking at the whole picture of how the confrontation occurred - rather than the result.