Mum
What not to call ones chemistry teacher in class, or any other time for that matter. Unless, by some strange quirk of fate she is your mum, but that would make you her uncle or something.
written by Na*h Dog*, approved by Log

Another situation in which you should never shout mum - and there are many - is when you have been stung by a bee. And you are in your shorts, during a P.E. lesson. And you are running towards your teacher, who is a man.
Although the hysteria will get everyone sent to the changing rooms early, you will never convince anyone that your mother isn't a big hairy man.
written by an*nym*us *ser, approved by Log

I didn't say "Mum", but after being pushed over by another kid outside the school gates, I walked all the way home, bawling my eyes out with my hand up in the air. Kudos minus infinity.
written by Z *avi*, approved by Ponky