Fortunately I only had to deal with this particular user due to covering for a someone's holiday, but I believe they're still at the company, and still batshit.
So, I forget exactly what I was doing that day, it might have been a file server migration, anyway, I was going round all of the desktops in a company, and I reached a desk sat just outside the MD's office. The user wasn't there, so I sat down and started doing whatever my job was that day.
Well, I tried to do my job, but for some reason the mouse wouldn't work right. It didn't move smoothly, and wasn't tracking right. So I turned over the offending rodent, and found that someone had sellotaped a 2p coin to the bottom, I ripped it off and continued.
The user eventually came back, walking across the office yapping on their iPhone the whole way. Eventually they finished their conversation and asked what I was up to, I explained, and added that I'd fixed their mouse by removing the coin. They replied that they were "allergic to electro-magnetic waves" and that the 'copper' 2p was somehow supposed to help.
I informed them that the best way to avoid exposure to harmful electro-magnetic waves was to wear sun-screen and left them to their delusions.