So say, imagine that someone said on IRC that he had screwed someone else's and how you shouldn't say it 'cause of netiquette?
If what one copies isn't a lie I don't know why shouldn't one be allowed to copy it, even further when in context...
Just because it doesn't say in a formal document signed by the king, prime minister, president and a notary public that you can not do this and that, doesn't mean you can do what you please without regard to others.
It's simple, when you write it down express that you don't want it quoted, although being in a public channel might not be the best place to do it, it's a question of intelligence after all, if you don't want others to use your words against you you should pick those to whom you say them