Jay, I dont think you have it quite right. Registering your designs may help you if someone rips your shirt, but not registering does not void your ownership as the creator.
Check out this chunk of text from copyright.gov:
"Copyright protection subsists from the time the work is created in fixed form. The copyright in the work of authorship
immediately becomes the property of the author who created the work. Only the author or those deriving their rights through the author can rightfully claim copyright."
Your illistration of Guy2 having the legal copyright because he registered it is simply false. Registration is optional:
"The way in which copyright protection is secured is frequently misunderstood. No publication or registration or other action in the Copyright Office is required to secure copyright. There are, however, certain definite advantages to registration."
and
"In general, copyright registration is a legal formality intended to make a public record of the basic facts of a particular copyright. However, registration is not a condition of copyright protection. Even though registration is not a requirement for protection, the copyright law provides several inducements or advantages to encourage copyright owners to make registration."
This page has most of the good info:
http://www.copyright.gov/circs/circ1.html
It also outlines the process for registering your copywrited work and has all the forms. Costs $30 I think
Also,
jdr8271 is correct when he says only the owner can file for the design: "Only the author or those deriving their rights through the author can rightfully claim copyright."
When it comes down to it, the only way to stop someone from using your designs is through a private lawsuit, and if it goes that far you will need to demonstrate that you created the work and this guy is infringing. A copyright registration may help, but it alone is not proof.
Martin