F which comes from the internet slang, Press F to pay respects. It means to pay respects to something or someone in a game after they have failed at something. It is simplified by just typing F. It is also used as a meme on social media, especially used by gamers since its origin story starts from a game.
The game in particular is Call of Duty: Advanced Warfare released in 2014. During a memorial cut scene, the player is asked to press F in order to pay respects and this started a meme about the sad moment turning into one full of satire by asking a player to press F.
Furthermore, the term can be used in the phrase “Can we get an F in chat” where the f means to fail. Moreover, it also goes back to the previous point whereby respect is paid to the failure committed.