This sort of thing is everywhere. Children and adults will often say “no offence” before or after saying something crushingly offensive, or introduce a nasty remark with a phrase along the lines of “I wouldn’t want you to think I’m nasty, but…” Politicians sometimes say “with respect” to interviewers before making clear their contempt for the question. There’s nothing new about rhetorical devices that let you have your cake and eat it—“not to mention the weather” gives speakers the chance both to mention that blasted weather and to leave it out. But the subgenre of such remarks that tries to dictate in advance how its targets might categorise it, and by extension the character of whoever might be saying it, does seem to be a recent and peculiar development.