The shout comes from Old Spice's famously loud and comedic television advertising, which turned exaggerated masculinity into a joke by having its spokesman bellow rather than simply describe the product. That over-the-top delivery made the single word easy to lift out of context, and it spread online as a reaction sound for moments of sudden strength, confidence or absurd bravado. It endures because the performance is instantly recognisable even without the advert, and because one drawn-out word can sell a punchline faster than a full sentence.