"F" in Internet slang is often used as a way to pay respects or show sympathy. It originates from the video game "Call of Duty: Advanced Warfare," where players are prompted to press the "F" key on their keyboards to pay respects at a funeral.
In the scene, players are prompted to press the "F" key on their keyboard to pay their respects at a funeral. The phrase has since become a meme, often used humorously to acknowledge a failure or express condolences in online discussions and social media.