I work as Tech Support for a small software company so I get quite a few calls a day. I thought you might want to share my laughter at this one...

Me:This is Russell
Customer: Can you tell me what my user name and password is so I can download an update from you website?
Me: Sure. First of all, the user name and password are both case-sensitve.
Customer: Ok.
Me: Your user name is (whatever) and your password is (whatever).
Customer: Ok, Thank you. I'll give this a try.
Me: You're welcome. Bye.

Five minutes later I receive a phone call from the same customer.

Me: This is Russell
Customer: Can you tell me what the password is again please? I must have it wrong.
Me: Sure, it's (whatever)
Customer: And what was the user name again?
Me: It is (whatever)
Customer: Oh, I'm sorry. When you said case-sensitive earlier, I wrote that down as the user name. Do you mind holding on the phone while I try this to make sure it works?
Me: (Trying desperately not to laugh hysterically) Sure, not a problem.
Customer: Oh, that did it. Thank you
Me: (Wishing I could really say what I was thinking). Have a nice day, ma'am. Bye

I've run into some pretty funny instances but I don't think any have been this comical!