More office fun:
If senior management in our company wish to let all staff know of some important event, they send an email to **All Users. I discovered an evil little trick you can use it for:

If you have a load of pictures of one of your drunken colleagues making a fool of himself at a party, scan them and e-mail them. Put **All users as the subject but just BCC the message to a few select friends - including the person you want to humiliate. Watch the panic as he opens the email, thinking you've sent it to everyone.