When your game of Fortnite becomes a cluster fuck in Tilted towers, ending in you and your squad dying first which causes you and your squad to rage quit and consistently refer to the game as "Fucknite" instead of the actual name of the game.
A simple amalgamation of the words 'Fuck' (to engage in sexual intercourse), and the slang definition of 'Stag'(a raging erection). Originating from the squallid rural town of Gympie in the great south east of Australia, 'Fuckstag' is most commonly used to describe one who is of low moral calibre, social standing or who is poorly regarded by his peers.