People who don't seem to understand how lifts work.
1) Pressing the up and down button when your waiting on the 8th floor of an 11 floor building will not make it come any quicker, just annoy passengers who are already heading UP when you want to go DOWN.
2) Said idiots getting into a lift you are in that is heading up and asking "going down?" as they step in with that "derp" looking smile on their face, "No mate the big [Poor language removed] illuminated arrow pointing upwards should have been a minor hint".
3) Getting into a lift, it has the exact number of floor options in relation to the size of the building, if the ground button is the only one lit up, then evidently another passenger has conveniently already selected this option so why, why, why you [Poor language removed] melt do you feel the need to press the ground button again!