Random couch question: why the hell is it socially acceptable to insult someone with the qualifier 'no offense' tacked on?

No offense, but your house is really strange. The truth, this person thinks my house is strange. The qualifier, I'm not supposed to be hurt or offended by this statement.

Statements meant to offend, preceded by other people telling me how to feel, are somehow even more offensive. Even though the qualifier is thrown out there as a way for people to tell you 'I don't mean to insult you' that doesn't make the statement any less insulting, and somehow makes me look like the bad guy when I get insulted by the insult as if I failed to follow instructions!

Sorry. That's been bound up for a while. Discussion?