Wel i must say i agree with most of the above, but in my old age (27) i must say i am a lot more tolerant then 10 years ago...but there will always be some things that you can't tolerate when on the road, some of mine what i can think of now....
One taillight/headlight, worse still brake light and incorrectly aimed headlights. Worse people with no brake lights at all who never check reflections and are just oblivious, i once pulled up beside a guy and informed him he had no brake lights to which he replied,
"well you better be careful then"
People who sit in the wrong lane 10mph under the speed limit then sign at you for flashing or undertaking
Braking for a speed camera at the last minute when already doing the correct speed limit anyway
Bad parking, inconsiderate idiots who don't leave enough room when there is and moan when ther car gets damaged
People who block KEEP CLEAR markings so you have to sit there and wait AGAIN!
Drivers who don't say thank you when you go out your way to be considerate
Wrong timed/incorrect/not needed signal
My wifes driving Lol!!
Jus some of my pet hates, i'm sure there is plenty more but thats jus what i could think of for now!