NPO stands for "nothing by mouth." Patients are kept NPO before a procedure or if they are very sick incase they are at risk of aspirating their food.
A man came in around midnight with a chief complaint of "I need a chest tube." I asked him how he knew this. He said that he was in a fight that day, and has had bad chest pain and shortness of breath. He went to an urgent care at 10 pm, and they diagnosed him with a pneumothorax (hole in lung). They told him that he needed to go to our trauma hospital to get a tube in his chest to reexpand the lung. I asked him what the delay was....what he was doing for the last 3 hours. He said he knew we weren't going to let him eat before the chest tube, so he went out to have a nice big steak and a few beers before the procedure!
This reminded my attending of an even better story. A man walked into the ER holding his abdomen. It was quickly identified that he had been shot in the stomach. He gave no details, and was taken to the OR emergently. In the OR, they found a hole in his stomach. Visible in the hole was fresh chicken nuggets and fries! When the surgeon asked him about the nuggets post op, the patient said "last time I got shot you guys didn't let me eat for days, so I went to McDonald's before coming here." It takes a tough, dumb mo fo to head to micky dee's being shot in the abdomen.
-ER Doc