One of the best rules in conversation is, never to say a thing which any of the company
can reasonably wish had been left unsaid.
i can't be sure if i understand the quote right. cud anybody help me with it, please? thanx in advance..
'Company' in this context means 'the people present'
Basically it means 'When talking with others, don't say anything which will be taken as rude by anyone involved in the conversation.'