OP, I am glad you put a stop to it.
As I was reading all these posts I was thinking...wow...no one every borrows things from us then I was like..hey...they did (or used to). DD's old bff lives across the street and her mom used to borrow DH. DH is a computer guy. So he has spent hours over there cleaning up virus's from their computer due to the usage of their teen son. He warned them about it, and it happened again, and again. They once asked what restaurant DH liked, so I figured hey...they eant to get him a giftcard.

Well nothing ever showed up. Now during this time period DH was self employed and he charged 40.00/hour for these services. Now the parents new this.
Needless to say I put my foot down. Whenever they would ask I would say, DH is busy working and gets home to late, and would repeat as needed. They finally got the hint when I saw the Geek Squad car in front of their house.
Now, his parents to it all the time to him and his brother...but they are parents so what are you going to do. My brother also did for my DN usually, but sometimes for his computer. It go to the point if we went over there for a bbq or party I said DH was sick, since everytime DH walked through the door, he was asked to work on a computer. I got PO'd. The straw that broke the camels back was when we were there sitting Shiva for our eldest brother. I mean seriously?? I really would like to have my DH sitting next to me and not in the basement for 4 hours!
Now my DH tells them to drop the cpu at the house and he will get to it when he can!!