One of the easiest ways to let people know that you want to be left alone is to wear a pair of headphones. Either you won’t be able to hear other people, or they will assume that you can’t hear them. It is an easy way to show that a character is trying to drown out reality and other people. This trope is either used symbolically, where the headphones are a side effect of their isolation, or deliberately when the character does this on purpose. (TVTropes)
