The robots.txt file is a file you can include in your site directory to help prevent most spiders or bots (automated programs) from ‘crawling’ or indexing certain directories. Here someone (on the Lastfm crew http://www.last.fm/robots.txt) decided to have a bit of fun with it, note the last set of rules.

User-Agent: *
Disallow: /music?
Disallow: /widgets/radio?
Disallow: /show_ads.php

Disallow: /affiliate/
Disallow: /affiliate_redirect.php
Disallow: /affiliate_sendto.php
Disallow: /affiliatelink.php
Disallow: /campaignlink.php
Disallow: /delivery.php

Disallow: /music/+noredirect/

Disallow: /harming/humans
Disallow: /ignoring/human/orders
Disallow: /harm/to/self

Allow: /