You're thinking of two different code-on-shirts episodes here (Federal export controls on cryptographic software and entertainment industry litigation over DVD

You're thinking of two different code-on-shirts episodes here (Federal export controls on cryptographic software and entertainment industry litigation over DVD decryption software), although both of the shirts may have involved Perl code. "This shirt is a munition" is from the cryptography export controls issue and DeCSS is from the entertainment industry litigation issue.