Prevent users from including their username in their password I'm aware of the Password Policy module that has a number of features for forcing the user to constrain their passwords to certain criteria, but this module does not contain an option to prevent users from including arbitrary strings in their passwords (such as their own username). 

Ex. User bob receives a validation error if they try to change their password to anything that includes the string "bob", such as "889bobisthebest99".

Does anyone know how to code custom functionality to achieve this result for Drupal 7.5 or a module that already does what I'm looking for?
I found that the Password Policy module actually does have an option to prevent the user from including their username in their password. The broader issue about how to restrict arbitrary strings from a user's password still stands though.