Rats are not off-topic in ESL as you will be able to infer from the notes on that Chinese "school". You may enjoy this delicious food in their school canteen. BTW, I have taken the liberty to correct two errors/mistakes in your own English text below, Mr. Nadiff Sbeaker!

Having said that, rats should be off - topic, We should concentrate on English, please. For crying out loud!

I didn't make a mistake, it can be with or without the hyphen. The frightening thing is that you should know that if you call yourself a teacher. As for the other 'pick-up.' I put a comma instead of a period. I won't bother to explain.

Expert Answers
pohnpei397 | Certified Educator

If something is off topic it is not related to the subject or topic that it is supposed to be discussing.
There are a number of different situations where you might encounter this phrase, but it basically always means the same thing.  For example, if I assign a student to write an essay on freedom of speech and he starts to write about how the US government is spending too much money, I will tell him this is off topic.  He was supposed to write about freedom of speech, not about how much the government is spending.  Someone can also introduce a subject that is off topic in an oral discussion.