The phrase 'I Want to Cum Inside Rainbow Dash' is a notorious piece of internet history that originated within the 'Brony' subculture on imageboards like 4chan. It stems from an explicit and highly detailed copypasta where a user expressed an obsessive, hyper-fixated sexual fantasy involving the blue pegasus from My Little Pony: Friendship is Magic. While controversial and shocking, the phrase evolved into a symbol of ironic 'cringe' culture and post-irony, often used by trolls to derail discussions or by internet historians to reference the more extreme corners of 2010s fandoms. Today, it is primarily used as a reaction to overly obsessive fan behavior or as a shock-value punchline in niche meme circles.