The agents rarely wear gloves when handling evidence at crime scenes. In fact there are several instances where an agent is warning others about not contaminating a crime scene when they themselves are handling evidence with their bear hands.
A number of times in the series the agents assume someone is their suspect because they have the same caliber gun as the murder weapon, and its almost always a 9mm. Yet the 9mm is by far the most common handgun caliber in the world, so arresting someone based only on the fact that they own a 9mm is something that would not actually happen, it is the weakest kind of circumstantial evidence.
FBI Agents wouldn't have their hands in their pockets when talking to people on the street. (As happens frequently throughout the show)
It's considered unprofessional and also delays reaction time in the event of an attack.
It's considered unprofessional and also delays reaction time in the event of an attack.