Fucknite is a convenient yet very sexual way of saying the popular video game, "Fortnite". This term is used when that person is trying to be funny and can either be successful or not.
Example 1: Hey Nick, would you like to get on fucknite right now?
Example 2: You ever heard of that game, fucknite?
Example 3: Ew did you hear that Chris plays fucknite!?