The password that you use for every website, email account, facebook, twitter, everything. Having a 'life password' is not a good idea, but everyone does it.
My friend found out my life password and wrecked my facebook account, stole all my paypal money and emailed offensive images to my mother.
The progressive increase in both the number of different passwords you need to have at work, and the number of times you have to change them. Each password usually has unique requirements, which along with the frequent changes, makes it virtually impossible to remember your passwords. Resulting in a word document on your desktop call "PASSWORDS.docx" that reduces the security of ALL passwords to zero.
"I just changed my login password for the 15th time this year. But due to this password creep I've forgotten what it actually is. It used to be the same as my copier password but that's only been changed 8 times. Anyways, I forget what that one is too, so I have to go to my password document on my desktop to find them."