The 'That's a Penis' meme originated from the sitcom 'How I Met Your Mother' during the episode 'Aldrin Justice.' In the scene, characters react to an architectural model designed by Hammond Druthers that bears an unfortunate resemblance to male anatomy. While the original line was delivered by a student in the show, the reaction GIF became an internet sensation for its blunt delivery and perfectly timed realization. It is widely used across social media and forums as a reaction to anything that looks unintentionally phallic or to call out someone making a suggestive mistake. The meme's longevity is sustained by its versatility in awkward situations and its status as a quintessential 'once you see it, you can't unsee it' moment.