/** debug **/
console.dir( myObj );
/**/
and a corresponding YUI Compressor command-line argument "-rmdebug"
$ java -jar yuicompressor-2.5.2.jar -rmdebug script.js -o script-min.js
Update: Ok, so.. after I posted this, I searched the yuicompressor feature request list, and natch, somebody requested this - at least the debug-one-liner version: treat as debug any line that is prefixed with ";;". YUI Compressor Feature Request: remove debug code.
;; console.dir( myObj ); //double-semicolon prefix indicates this line is for debugging