I've had too many users over the years, mainly senior management, who've bypassed IT and bought their own kit then expected us to support it.
Worst was an MD who bought a Sony Vaio laptop from Dixons (as it was then). 13 months later Windows had to be reinstalled, no he didn't have the driver disk(s), that was our problem not his. It turned out these particular laptops had been thrown together by Sony Japan from the parts bins for DSG.
No drivers were to be had, DSG weren't interested as it was out of warranty, Sony Europe said it was Japan's problem, Japan said it was up to DSG as the retailer.
His so-called "good buy" was in the bin after just over a year.
The same MD bought an early wireless mouse for himself and one for his oppo, they complained they were getting random mouse movements with these expensive new devices. Their desks were literally back-to-back with just a partition wall in between and the mice had no way for changing channel or encoding.