We had an email from a very senior person, she was known for being fierce, which said 'please can everybody make sure their email signatures are uniform in Colour, either black or blue'.
I changed every single letter to a different colour (and its a long email signature, several lines of text) and forwarded it to a colleague for a laugh...
Except I'd clicked Reply, instead of Forward. Panic set in.
Got a response a few minutes later:
'LOL. Very funny.'