Stop the cap comes from internet slang in which cap means a lie, so the phrase is a blunt way of telling someone to stop lying. It spread through short-form video, reaction clips, and meme soundboards, where creators used it as a quick verdict on exaggerated claims, fake stories, and overconfident boasts. Because the wording is short, instantly understood, and easy to drop over almost any clip, it stayed in regular use long after its first viral wave, especially in gaming, sports, and comedy edits that thrive on calling out nonsense.