My Two Errors that made friends
Ages ago - when Windows 95 was king:
I had users who wanted Windows 97. They really wanted an upgrade to Office 97 from 95, but they did not think that way. So for a select few I would do the proper upgrade and then put a logo.sys file for Windows 97 (the version that never made it out the door) on their system too. DELIGHTED USERS and I let them smile for a day or so before I brought them on my joke and straightened out the logic, which they appreciated all the more.
One user was a constant complainer of error messages on her system. Every single one drove her nuts but she was OK so, with the permission of my boss, I put a screen saver on her system that did nothing but populate it with error messages. Wonderful. Walked by and asked " any problems today?" She caught the joke too.
YOU do have to be careful doing this but if you laready have a working relationship, a bit of fun can be had and this, too, is good customer service.