A coveted and well-tended accessory of a character that makes him attractive or at least interesting to other characters, if only in his own head. This can be anything: a well-groomed mustache, a bizarre body part, a favorite hat, a personality trait, or a bow tie. For maximum humor, the actual draw of the item may be completely non-intuitive to the audience, but make perfect sense to whatever minor passerby appears on the show.
At some point in the story the character invariably loses it (or someone else does) and rapidly becomes inept or clumsy at whatever he usually does with ease, while everyone notices something is 'off' about him. Thus the item takes on a Magic Feather effect, even when he's reassured by the cast it shouldn't make any difference. Whether or not he learns an Aesop about it has no effect in his immediately retaking it once it's accessible again.
In an episode of Lupin III (Red Jacket), Jigen becomes unable to shoot straight after losing his hat. He tends to wear it rather low, and later it's explained that the trademark notch in the brim is how he usually lines up his shots.
An episode of Keroro Gunsou has Giroro becoming clumsy and a lousy shot after having his trademark belt stolen. Likewise, he loses a sumo match with alien rodents by not being allowed to wear it. Later we find out it's also because he keeps a picture of Natsumi in it.
In one chapter of the manga, we find Keroro's "Keron Star" emblem bestows great charisma on the wearer, which is almost completely nullified by Keroro's abrasive personality. Hilarity Ensues when Giroro's pet cat steals the star and becomes the new platoon leader.
Mori from Ouran High School Host Club is an odd case since his Charm Point is another character. When the club tries to instruct a delinquent that a Charm Point can work wonders for one's image, they bluntly point out that without Hani around people would see Mori as just a huge scary thug who barely talks, much to the latter's distress.
Detective School Q, Kazuma Narusawa claims at the beginning that he can't keep his thoughts straight unless he's wearing his lucky hat. He grows out of it later, as his self-confidence grows.
Atobe of Prince of Tennis has a beauty mark on his face that he refers to as his Charm Point. His voice actor even recorded a song about it.
Of course, there's Major Armstrong from Fullmetal Alchemist who, believing that his (admittedly stunning) physique is desired by everyone, will take any opportunity to show it to anyone (including Scar in the middle of a battle. Scar was not amused.)
Bond in Dr. No sees Honey Ryder's broken nose as this, and secretly hopes that she won't fix it in a surgery as she plans to.
In one episode of Columbo, the title character's wife throws away his trademark rumpled raincoat and buys him a new one. To his dismay, he can't concentrate while wearing the new coat and keeps leaving it behind at scenes. In the end, he apparently convinces the missus to let him have his old coat back.
Seinfeld actually had a story arc about Kramer's attempt to retrieve a jacket that supposedly had magical powers over women.
Cheers had Sam's "lucky beercap," from the last bottle of beer he drank before he went on the wagon. He loaned it out and the person lost it, and he became klutzy and despondent.
Specifically, mustaches sprouted through sheer force of will.
An episode of Rocket Power centers around Twister losing his cap, then claiming that it made him who he was. Just as he grew to accept the fact that he didn't need it, the cap came back.
Does luck count as an example? Because in Extreme Ghostbusters, Garrett "loses" his "luck" owing to a curse placed on him by a leprechaun. Not long after, things start to go wrong. Including Garrett nearly being beaned by a falling brick. And breaking the back window of the Ecto-1. And accidentally breaking a flask of phlebotinum that Egon was working on. Worse still, the other Busters (apart from Egon) were buying into the bad luck thing, with Garrett eventually beginning to agree. So, Egon gives him a flask of phlebotinum "by-product" to drink which should restore his luck — and after drinking it, Garrett appears to have his "luck" back. Egon's "by-product" was actually flat grape soda. Oh, the joys of psychology!
Chuckie's bright red hair on Rugrats. When his hair gets accidentally dyed black, people suddenly stop noticing him. At first, Chuckie wanted to lose his hair due to it bringing him unwanted attention, but then he realized that he missed being, well, himself.
Sokka from Avatar: The Last Airbender believes this about his boomerang, and as such is crestfallen when he loses it, and spends the whole episode trying to find a new "thing". As in many other examples, he comes to accept it by the end of the episode, then gets the boomerang back.