Mine is - lazy work colleagues who think they are above others.
We have one at ours - it is forever taking breaks, putting itself unavailable without telling colleagues meaning we take its work. It is not at desk ready to work until 9:25, yet logs off at 5:30. It is forever moaning about being how busy it is, but taking no effort to get in early to catch up (if it really is that busy) - which leads us to the conclusion that it is actually faking an affront at being busy whilst it is just on its Iphone half the day.
Second to that - the managers we have complained to about said above, who have so far taken no action...