The registry, I always say, is an answer to the question, "What can I get you to celebrate your wedding? Do you have any guidance for me?"
Sometimes, the guidance you'd most like to give comes in the form of a negative ("We don't need pots and pans"; "Crystal isn't really my thing"; "We have no room for picture frames and vases"). How do you say what you don't want? Normally, you can't. You simply neglect to register for pots and pans and list Danish Modern stuff instead of crystal, and hope that people get the hint.
Here's another tactic I ran across: Register for these "don'ts" anyway -- but mark them as "fulfilled." Isn't that genius?
Of course, it's not foolproof, but it's worth a shot!
What are you hoping nobody buys you?