I completely. completely messed up MySQL. Badly. I wiped out the data directory (/var/lib/mysql in Debian) and the went to remove mysql …
apt-get remove --purge mysql-server

That only deleted something like 86K. dissapointing. It looks like “mysql-server” is a shortcut pointing to the latest version of the software. The real software is found  under the name “mysql-server-50″. So what made it happen was:
apt-get remove --purge mysql-server*

That’ll wipe out whatever mysql install is in place.