2 things that always get under my skin:
– People who feel the need to repeatedly say your name when talking to you (I know my name, you don’t have to point it out, there are other ways to let me know what you’re saying is directed at me – try eye contact!)
– Excessive use acknowledgements, such as “ok, ok, ok”. That sounds more like auto-pilot than acknowledging what you’ve said and you end up feeling like you’re talking to a brick wall.
It also bugs me when people are so set in their ways that you can’t even discuss alternatives – it is remarkably frustrating!