Ooh...too many to narrow it down to one.

My pet peeves:

As a driver, encountering other selfish and spatially unaware drivers. Also, meeting other drivers who think they own the road and drive up my ass.
As a shopper, lack of manners or general rudeness to shop staff/service staff. They are there to help and are not a lower class of people.
As a chivalrous man, the fact that acts like opening the door for other human beings are often taken for granted and not noticed. Manners cost nothing after all.