When a person listening to music through a pair of earphones is confronted another person and takes an earphone out of only one ear. This usually happens because they know the person who confronted them will only want to engage in small talk and, therefore, don't find it worth the effort of taking off both earphones.
Person 1: *spots person 2 after class* Dude, class was so boring today.
Person 2: *does the earphone maneuver* Yeah... it was.
Person 1: Yeah, so I guess I'll see you tomorrow!
Person 2: Later. *puts earphone back on and continues listening to music*