Before His Dentist Appointment
Brushing one’s teeth appears to be a non-annoying activity. Everyone is expected to brush twice a day, at the end of the day, in order for their dentures to stay white.
There’s a chance he boarded a plane early in the morning and didn’t have time to clean his teeth until he was in the air. At any rate, some passengers were irritated by it. Despite their best attempts to tell him to stop, the guy kept brushing away.