Respectfully show disrespect

I think smarmy is pretty good:

1 : revealing or marked by a smug, ingratiating, or false earnestness
a tone of smarmy self-satisfaction — New Yorker

I generally understand it to be use in a situation where somebody uses words or actions of respect, but in a tone of voice or mannerism that belies their sincerity. In other words, they are sarcastic about it—and it's obvious that they are mocking the person rather than actually meaning what they say.

Perhaps if they were captured on video or audio, somebody could take them to task (although it would be interpretive if they weren't over the top about it), but if their words were transcribed, they would seem to be spoken in a positive light rather than negative.