People that make lines hold up.
People that do not signal when they want to exit a roundabout.
The custom of saying "you are welcome". Admittedly this is very mild, but I mean, I did/said something, you said "thanks", why do I need to prolong the meaningless exchange by adding something on top of it? Of course I always say it (apart from when I am with close family) because of its cultural and social weight, but I wish it could be avoided entirely without looking rude or distracted.