It seems really rude to me that a friend or relative would ask to borrow a book, DVD, or CD, or something else and then never return it. What is the problem here?
When I've asked for the item back, the borrower has acted as if I was the one who was being rude to him. I loaned my bike to a friend once to use over a weekend, and he kept it, and the keys to the lock, until I had to actually go to his apartment and take the keys from him months later. He acted like I was accusing him of a criminal offense and I was the one who was being rude.
A Russian family once borrowed several books from me. One was Tom Clancy's The Hunt for Red October. A couple months later, I asked the father if he'd read Clancy's book. Yes! And he proceeded to talk about how much he'd enjoyed it, and his wife had enjoyed it too. So, I asked for it back. He looked at me surprised. "But I thought it was a gift." I asked him if he understood what "borrow" means in English, and the word "loan." Turned out, he understood loan because of bank loans, but borrowing something was a new concept completely. I did not loan anything more to these people although they asked to borrow books from my personal library on a regular basis.
As pet peeves go, this one tends to be a big one for me. I enjoy sharing with my friends. It pains me when my ownership of something isn't respected. It boggles my mind how someone could so forget or ignore the relatively small responsibility of returning something that's been borrowed from someone. I don't understand this.
A gift is something given with no expectations whatever. Once I've given the gift, it belongs to the receiver. A loan of something means that the loaner retains ownership of the item and the borrower only has use of the item for a short period before returning it to the owner.
People with poor boundaries tend not to respect the terms of a loan. Or someone who's not been brought up to respect other people's belongings. Or someone from another culture that doesn't understand the concept of borrowing an item or a loan. I've even heard the explanation that an ex-boyfriend or ex-girlfriend may keep something of yours simply to have something that belongs to you -- a connection to you.
And then there are the people like my relative who helped himself to my LPs. He believed that because of his position in the family he was entitled to keep whatever he wanted of mine. I discovered this years later, after his divorce, when I was visiting his ex and looking through her LP collection. In it I found several of my LPs that I had noticed missing earlier -- I had written my name on each LP as well as the album covers. They both knew those LPs belonged to me. I made a list of the LPs she had in order to replace them but said nothing to her about them. I understood that my relative had kept my LPs for himself and that the collection had been split during the divorce. I never again trusted that relative with any of my belongings, and have always kept in mind that he lied to me.
As for sharing my possessions, I rarely share now. My personal libraries of books, DVDs, and CDs remain within my home. I make no loans, and I also do not borrow from others. But I do continue to give gifts.....