ppl who have to talk in the middle of the road or exit.
it anoyed the poop out of me in highschool. there was 1 exit gate for the bike's and there would always be a group standing in the middle of that exit.

edit:
forgot my biggest one:
kids on bike's, playing music through the speakers of theire phone :l
get some earbuds for the loev of god! we dnt want to hear yr music