*disclaimer: this may or may not have happened to me. I can neither confirm nor deny the following. :P

*phone rings*
Me: Hello, Helpdesk. Can I help you?
User: Yeah, I can’t seem to login to …
Me: Ok, let me just verify that your password works.
Me: *proceeds to log in with the user’s password. It works.*
Me: Ok I’ve just logged in with your password. Is your caps-lock on?
User: Nope, I’ve checked.
Me: And you are using the password I gave you yesterday?
User: Nope.
Me: *vomits blood* Why don’t you try using it?
User: Hey it works! Thanks!

(EDIT for clarity) User had assumed that a password that I gave him earlier for something else would work too. Wah lan eh. Why so dumb one har?