There's absolutely nothing wrong with yawning. Especially if you're going to cover your mouth while doing so. However yawning out loudly is not professional or courteous. I had to reprimand some guy who was seated not too far from me, one time, about yawning out loud like he had just woken up from his afternoon slumber. If you are going to yawn, then by all means do so, discreetly, you're not at home.
Clipping finger nails
I really don't understand when someone decides to clip their fingernails at their workstation, whilst working. Especially if said work space is shared. You have all the time in the world to do this at home yet you choose to do it at work..? It doesn't sound right. It doesn't look right. And, it'll never sound or look right. It is unhygienic and very distracting, especially the clipping sound. If you really have to clip your finger nails at work then rather go to the bathroom and clip them over a paper towel and then discard the towel by flushing it down the toilet. That way we are all spared the sight and sound of it all.
Taking shoes off
Gentlemen, this is highly uncalled for. Even if you're wearing socks. Even if we don't see under the desk. Even if your toe nails are clipped and your feet are clean. There is absolutely no need to take your shoes off. If your shoes are too tight then, you know to buy a size bigger next time and, in the mean time, rather let your feet suffer the tightness and claustrophobia.
Dirty pause tables
No one has a 24/7 maid, waiting on them hand and foot. So while you're at work clean up after you have finished eating and drinking in the pause area, canteen or any shared office space designated for food and beverage consumption. Some people are on the clock and every minute counts to them. So for someone to get to a dirty table, first clean up and then sit down to eat, by the time they take their first bite, it'll probably be time for them to get back to work. Be considerate.
Disposing of gum
Believe it, today I found a piece of gum stuck to the back of a cpu unit. People have little regard for their work equipment and a piece of gum stuck to a cpu unit can lead to serious damage of a computer. A cost that wouldn't be borne by the culprit but the company. There are bins provided and if you're far from a bin then you can always put your gum in a tissue and then dispose of it later. There is no need to be sticking it to the equipment, furniture, etc. Respect your work place.
PG: Man to man, generation to generation.