After retiring from the NCIS at the end of Season 3, Season 4 opens with Gibbs living in Mexico. He's sporting a light beard (which mostly just looks like he's been relaxing and hasn't cared to shave), and it honestly doesn't look bad! He rocks the disheveled look for a couple of episodes, but things take a turn when he decides to shave off all of his facial hair except for his mustache. Fans were confused, and years later, some even went on Reddit to ask when it would go away — though no one seemed to understand why he grew it in the first place.
According to Two Red Dots, the producers wanted Gibbs to look gruffer, so they told Mark Harmon to stop shaving. The end result was a look that screamed "substitute teacher" more than "no-nonsense cop," which ended in him shaving it only a couple of episodes later. Though its life was short, the mustache lives on in infamy.
