I had a colleague..
..that when someone managed to forget their password 3 days in a row, changed the user's password to "Iamadumbass123456" or similar. Another trick was giving a PITA user a password like $%^&dhKn4*.r5xTz-_ I've been tempted, but never been that unkind.
When the company I worked for was going through bankruptcy, some of the passwords were quite entertaining in a dark way. And I've had users that didn't want to give out their password because they were embarrassed by them. One big, macho guy had "69Kissypoo69" as I recall..