Take a standard sticky note and write your message on the sticky side!
Take a piece of tape and make a little loop for the other side.
When your friend/boss/co-worker/brother-in-law is leaning forward in their chair to type in an instructable/status update/email/command to vent excesive pressure within the reactor core - Stick the note on the back of their chair.
When they next lean back in smug satisfaction that the world now knows whatever status it is that they posted or that the reactor is not going to melt - the sticky tape takes over and that note is on for the rest of the day!
And at no time did anyone have to get slapped on the back!