I used to work somewhere where locking your screen was important, as the company dealt with customer financials. So we would prank those who left screens unlocked all the time. One day, one of my co-workers walked away and left his screen unlocked. I proceeded to change his keyboard layout to Dvorak and left it unlocked, thinking he would be right back. He got caught in a very long discussion and his screen locked from being idle too long. When he came back and unlocked his screen, password was wrong so many times, he for locked out of his account. I had to tell him what I did and he had to explain to the network admins what happened. We both got a slap on the wrist for that one.