Conduct unbecoming an officer was an offense that Starfleet officers could be charged with.
In 2152, Jonathan Archer bluffed Plinn by suggesting that conduct unbecoming an officer and dereliction of duty were grievous offenses on Enterprise NX-01, warranting the death penalty. (ENT: "Precious Cargo")
In 2375, Tom Paris was found guilty of insubordination, unauthorized use of a spacecraft, reckless endangerment, and conduct unbecoming an officer, offenses for which he was sentenced to thirty days in USS Voyager's brig. (VOY: "Thirty Days")