Drupal core hacks - thinking about it?

Funny results from searching Google for ‘drupal core hack’:

Do not hack core | drupal.org
29 Jan 2009 … “Do not hack core!” This phrase is commonly heard in the Drupal community. There are even t-shirts made with this phrase and this cannot be …
drupal.org/node/144376 - 16k - Cached - Similar pages

Documentation: Info on Core Hack [...]