What is a good word to descibe someone who refers to you as the expert in a sarcastic way

I think "condescending" would be an apt description.

Or really, "unfair" might work too, as it is pretty unfair he'd give you so much trouble over one mistake, when I assume your advice is typically helpful.

EDIT: Also, I think the word you used yourself, "sarcastic", is an equally good word, if not better! Because that's exactly what his remarks are. Keep in mind to be careful he isn't just joking; there may be no bad intentions, and it's entirely possible he doesn't understand his teasing is bothering you. :)