My partner is foreign from another country in Europe but his grasp of the English language is very good.
So I've noticed he has this annoying quirk where you'll ask him something and instead of replying 'yes' he'll reply 'obviously' or 'yes, obviously.' I've told him it comes off as rude and sarcastic, and all he needs to say is yes.
I've seen him do the same with 'of course' instead of yes, except he tends to catch himself if it's in a shop or something/in public as though he does realize it's off.
It always reminds me of this clip from Downton Abbey where the waiter says 'obviously' and gets told off for being rude!