Cute little fang

Cute little fang, also known as the "Moe fang" or"Tsundere fang", is a character trait present with, most commonly female, anime and manga characters in which they have a small triangular tooth showing on the edge of their mouth. While the protruding teeth were already a well-known trait for certain character types amongst fans for decades, the trope did not become a popular meme until 2017.

Basically, a character's protruding teeth are played for unconventional cuteness and usually some level of contrariness. For maximum cuteness, at least one fang will be visible at all times, even when the character's mouth is closed. These often indicate, generally, that the character is mischievous, slightly hostile, or a trickster, but not actually "bad."

Cute little fangs are pretty much a standard feature of cat girls, cute monster girls, and other character types.

Usually limited to comedies. Does not normally apply to Western-style vampires (they do have fangs, but not the endearing kind).

Background
Snaggletooth, or Yaeba (八重歯) in Japanese, is the term given to human teeth, especially upper canines, with an uncommonly fang-like appearance. According to the Online Ethymology Dictionary, the term snaggletooth already dates back to the 1580s as a term for "having crooked, projecting teeth". In 2013, Yaeba became a trend in Japan where teenage girls and young women would undergo dental procedures to have their upper canines capped.

Well-known cute little fang characters

 * Tsuruya from The Melancholy of Haruhi Suzumiya
 * Kirino Kousaka from OreImo
 * Satania from Gabriel DropOut