Years and years ago when I worked at IBM, I added a panic button to all the dialog boxes in an internal testing program. When hit, it would cycle through several remarks (stuff like "Don't hit this button again" and "I thought I told you not to hit this button").
And for the past fourteen years I've included an HTML comment on some of my webpages and I've only had one person find (or at least, one person find and comment about it).
Back in the mid-90s I had a hidden Easter Egg in a Java Applet (the next big thing, you know) that expressed my frustration with the language even back then ( http://www.conman.org/people/spc/refs/search/search.hp1.html )
Shortly after that, I added another one in the HTML page for the rewrite to that product (no longer a Java Applet) that, amazingly enough, people found and tried to use ( http://www.conman.org/people/spc/refs/search/search.hp2.html ).
And for the past fourteen years I've included an HTML comment on some of my webpages and I've only had one person find (or at least, one person find and comment about it).