to be completely fed up with somebody who is a total bitch

[CrazyTights]

Just that really....f'ing p'd off with a colleague. Thank god they are retiring in a couple of months - I can't wait as they are a two faced bitch.

has something specific happened.

Well no, of course you are not unreasonable. Anyone would naturally be pissed off working with a horrible person. Look forward to a mini celebration when they leave for the last time though!