I never really had any annoying co-workers, but there was this student at the university that I attended that was pretty extreme. In my country students get a certain allowance when they attend the university. It will cover a cheap dorm-room or rental and food, but not much more. It used to be that you could get this allowance indefinitely, now you have 6 years for to get a masters (which is nominated to take 5 years, so you get one year for failing classes, or spending extra time on your thesis). This one student, let's call him M, had been at the university for about 12 years when I was there. Rumor had it that he had a car accident in his third year, which left him brain damaged. In any event he was covered by the old policy and could get the allowance as long as he wanted. He had absolutely no short term memory. He decided in his wisdom that he would continue his studies (physics) and his counselors supported this (why I cannot fathom). M never, ever took a bath or shower. I guess he just forgot. So he smelled really repulsive. His hair smeller like fat that has gone really, really bad. I doubt he washed his clothes. Whenever he was in the classroom (and we all had classes with him, he took them over and over because he kept failing, so you'd run into him at one time or another) we had to open all the windows just to breathe. When I went to grad school and became a TA I lived in constant fear that he would take one of the classes I taught. I mean, what can you do, he would not be able to solve the problems, so he needed the teachers constant attention, but if you failed him, he'd show up next year and you'd have to deal with him all over again. I think that's why he passed a class once in a while.
He never took one of my classes thank God, and I'm sure he is still there stinking up future generations.