Speak as you would be spoken to
You certainly need to watch what you say in the classroom these days.
At one time, teachers could refer to pupils as numbskulls, idiots or wasters. Being proficient in linguistic denigration was expected of you and was even worn as a badge of honour among teachers.
However, you cannot use such language in these more politically correct days. Do you want more respect from your pupils? The way to earn such respect is to use appropriate language.
Some people will mourn the passing of the tongue-lashing teacher who could cut an upstart pupil into shreds linguistically, but it now seems more important to have due regard for the pupil's self esteem. Teachers can find themselves in trouble for using inappropriate language.
The General Teaching Council, that guardian of professional standards, will haul you before a disciplinary committee. Yikes. Racist, homophobic or religious language designed to insult pupils are all taboo. Insults directed towards the members of a pupils' family could seriously damage your health. Who wants a visit from an angry parent bursting in through the classroom door?
Yes, I know that often pupils' behaviour might make you want to do it, but obscene language should never be used. Haven't you told the pupils often enough that they ought to have a sufficiently wide enough vocabulary not to use such words? A complaint to the police and a visit to the local police station would sully your otherwise perfect reputation.
Try to attack the poor behaviour, not the person. Respect the pupil as a person at all times. Using appropriate language is likely to engender respect between teacher and brat - sorry, inappropriate word.
Linguistically, as a professional person you are expected to remain cool and control your tongue, even when under extreme behavioural fire.
What sort of language should a teacher use? To obtain the best from pupils, the language should be warm, encouraging, available and supportive. Cold, inflexible, offensive or discouraging language should not be used.
You are in the communication business trying to engage verbally in the best possible way with your charges.
So, however much you are goaded, angry, upset, annoyed, frustrated, appalled or insulted, please only use language of which even your maiden aunt would approve.