Congratulations, you found a collision.

What's meant by that is if you can find a source string that hashes to the same thing. Using ROT13 is pointless since it's trivial to generate those.

MD5 is only slightly harder.

Reproducing the message is not a collision. In a collision attack, you find a message that produces the same hash as another message. You can't take the exact same message and call it a collision. ROT13 is immune to collision attacks by its nature, and the humor is in the fact that its "immunity" comes from not being a one-way hash. It's immune...but it's also practically useless for obfuscating the message, thus it doesn't protect your message at all. Thanks for taking great pains to make sure the joke got ruined.