Make username Anon via checkbox?

Is there a plugin out there, or a tutorial or something, or a snippet of code someone could whip up, that would place a checkbox next to the comments field for posts so when a Logged-in (registered) user makes a comment, they can check a box to make their name say “Anonymous” instead of having their username show up? I need to make sure that an Admin could see it in the Dashboard however. Thanks!