Because I think he's trying to help him. No offense (i.e. just trying to help you by telling you that), you're coming off as strongly part of the bad cliche.
If it weren't for the spelling, i would assume bvanslyke was a British English speaker. In British English, "no offence" means "I am going to offend you now". It's generally felt to be the decent thing to do to warn people, you see.