The way I heard it was as follows. One night, Ken and Dennis were working late, arguing about what to call their new operating system. After many hours of hot debate, the finally decided to knock off around 9:00 and go for a drink. As they walked into their favorite watering hole (the BTL Rathskeller), the bouncer at the door saw their jeans and T-shirts and attempted to enforce the dress code (plastic pocket protector and belt-mounted calculator required) by pointing at them and saying, "You: nix!", meaning of course that they couldn't come in. And so history was made. . . (from a post on comp.unix.wizards)

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