My browser URL bar has received a few passwords, usually just a local computer password but occasionally something more sensitive. Makes me wonder about the permissions my collection of browser addons has.
I've also chucked a few passwords into IRC in times past. Fortunately non-essential stuff but really motivated me to sort out some better solutions (SSH keypairs, etc).
Plenty of times I've come back to my computer, typed my OS password expecting that it was locked, waited for my display's turn-on lag, and found that it wasn't locked (grace period). I type the password blind, but reserve the enter until I have visual feedback.
At least typical IRC clients don't transmit until hitting enter. Browser omnibars and Javascript can send away every keystroke as it happens. Now I want to search all my Google Docs for my passwords -- let alone other stupidity I don't care to share.
A long time ago in a lecture hall far far away a head of school was giving us a pre-exam talk of some kind. It was too all health science students. As he talked he logged into the system. With the projector showing what he was doing he missed the tab key and typed his username and password into the username field. I had a look round the room and no one else seemed to have noticed. On his desktop sat a folder titled "Exam papers" or something similar.
I've also chucked a few passwords into IRC in times past. Fortunately non-essential stuff but really motivated me to sort out some better solutions (SSH keypairs, etc).