Salty is the mood after a small defeat: not rage, just a lingering sting. "He's still salty that we beat him at the quiz." "Not salty at all that you went without me. Totally fine." (They are salty.)

The word has a long and varied history. Wiktionary's earliest citation for the "irritated" sense is from 1946, in Really the Blues, the jazz memoir by clarinettist Mezz Mezzrow and Bernard Wolfe, where two musicians are "salty" with a weak piano player. Dictionary.com traces the sense through sailors' language in the early 20th century into African American Vernacular English by the 1970s, and says the modern slang "originates in and was popularized by Black English". From there it spread widely online in the early 2000s.

Why salt? Wiktionary suggests the sharp, stinging taste, and perhaps the salt of tears shed by someone who's upset. Either way, it fits: being salty is a small, sharp, slightly embarrassing feeling.

It suits gaming and sport, where somebody is always losing and somebody is always ready to point it out. The usual reply to "you're salty" is "I'm not salty", which rarely convinces anyone.