What should be used for anonymous usernames?

More often than not, the best way to hide is to simply blend in with the crowds -- this also encompasses one's choice for a username. It is relatively simple to make a single throwaway account -- just come up with a username, and off you go -- however, if one makes throwaway accounts often, the task of thinking of a unique, and non-identifiable username can become a challenge. I would argue that poeple would often resort to using a pattern employing small changes for all subsequent usernames. Such patterns can be identified to a specific user if all users have their own unique patterns.

How can one reliably generate many unique-but-normal, and non-pattern-identifiable usernames?