I no longer work in an office environment but these things used to really irritate me -
People who constantly eat at their desk. I get sometimes you need to work through lunch but there were a few people in my team who would literally just sit eating all day, every day. Constant eating noises, licking fingers and the russelling of food packaging used to infuriate me.
People who would make fish in the microwave, thus stinking out the entire room for the rest of the day. Even worse if they then ate it at their desk
Constant charity collections - I give a monthly amount to charity by DD yet people look at you in horror if you dare to decline one of the several weekly raffles, dress down days or bake sale cakes
Monday Club - the serial offenders who regularly party all weekend then coincidentally fall ill on a Monday
I have more but I'll leave it there 