The best way to lose a friend is to offer to "fix" their computer.
When the damn thing won't even boot and he's lost all his files (all stored, unbelievably, on the Desktop) he'll hate you for ever.
I have a T-shirt that says,
"No, I WON'T fix your computer!"
Let him take it to the shop where some PFY will tell him that he has to reinstall Windows. He'll have lost all the driver discs so when the PFY tries then NOTHING will work! Then he can blame the PFY....
I'll do it for strangers, usually for money.