Demerit
A demerit was a penalty given to an ensign for bad behavior.

As of 2380, Ensign Brad Boimler did not have any demerits on his record.  ()

In the same year, Captain Carol Freeman remarked that her daughter, Ensign Beckett Mariner, was the most demerited officer in the fleet. ()

See also 
 Conduct unbecoming an officer

External link 
 

Starfleet
Punishments