h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Which cat did I let out of what bag?

greenguzzi, it's a trick!

See all the other messages on my page with the word 'cat' in the title

or
"Have you come across a thing called the tag yet? Well, you have now! It's a guideML tag which, when placed in a GuideML page replaces itself when viewed, with the username of the person viewing the page. So you see 'greenguzzi has really let the cat out of the bag....' whilst I see 'ictoan shadow has really let the cat out of the bag...' and anyone else will see their name.
It is usually used to provide a customised greeting on a page like 'Hello ' which would then be displayed as 'Hello greenguzzi' but there are some people, me being one, who have a twisted sense of humour and use it to confuse people

Hope I didn;t get you too worried!"

Very clever.
Ouch, ya got me!

If I had stopped to think about it (or if I had drunk a few less wines) I would have worked it out.

I have used it, but not in the sneaky way you did.