Practical jokes on the 'frame

I know 'someone' who once wrote a clist that displayed an exact replica of the TSO logon screen that was in use at the time.

The clist was named after a commonly used local function, so when the poor victim used it, he would think that he'd been booted off the system. He'd scratch his head, and try to log on again, but the "logon" screen would ignore his password. It was programmed to unlock itself after about 10 attempts.