because it is an annonomous(if you make it) forum where we are free to be retards with other retards like us. retards individually are weak, cowardly, and retarded. retards in groups are powerful, confident, and retarded.
Serious answer: age. The older I get the less of a fuck I give about what some random asshole thinks of me. If you like me, cool, if not, no skin off my nose. Does wonders for your confidence when you stop caring so much.
You have to figure there are so many times in life where being a retard matters. If you're holding a chainsaw and you're a retard, that can be a problem. If you're a retard while driving a car that can be too. On an internet forum being a retard doesn't really matter too much, so it's a good place to act like a spastic if you have to do it anywhere.
Plus this site wouldn't even exist if it wasn't for people confidently acting like retards, so it's only right to humbly pay tribute by adding your own to the pile instead of being a retardation miser.