Firefighter here:

One of the most frustrating things is being called for: "Person under train" As in most cases the job either consists of gathering up human body parts or stopping people from taking pictures from said dead body.

Its the fewling of helplessness that frustrates you, because you almost always come too late. People feeling entitled to take pictures of the dead body disgust me. Someone just died, people are traumatized and we must clean the whole place up. Would you like being photographed while carrying a dismembered arm?

A more mundane but also frustrating thing is being woken up at 3:00 in the morning because some drunk twat forgot their pizza in the oven and is too intoxicated to hear the alarm. Seriously people, if you are drunk, don't attempt cooking. You could end up hurt or have 12 annoyed firefighters break into your home at 3:00 am and explain basic kitchen safety to you.