Being a student makes things a lot funnier than they really are:
On a VAX system at the university I went to I had found a user that had left themselves logged in and left. Added to their login script an alias such that when they asked for a directory listing, it only showed files that were created 10 years earlier. (ie. showed no files in their account)
The sys-op/lecturer approached me a few days later, saying he "knew" I wouldn't have done such a thing!! And proceeded to tell me that the user is a niece to the head sysop in the parent university.
He apparently got in trouble for my 'trick' because some previous time he had also come across this user left logged in and had shifted all her files off into some system area so she had no files in her account.
She had cried 'help' to her uncle, uncle had talked to lecturer, lecturer explained to uncle what had happened.
This time, she complained to uncle, uncle sent a rocket at lecturer, and lecturer explained that he had done nothing this time.
Good thing I got on well with the lecturer.