When I was a kid people used to say something ultra critical to someone and then say "no offense" . It always struck me as odd. Just because you say "no offense" after being mean does not give you permission to be obnoxious. In fact whenever they would actually preface their insult with them not meaning to be offensive you always knew something insulting would be coming out of their mouth. It would be more honest to just blurt it out. If you think what you are saying may be offensive maybe rethink your words. Then there won't be any offense.