I do that all the time. I don’t see anything wrong with it. It’s not as if its food you’re going to taste, or clothes you’re going to wear, or a car you’re going to put miles on.
I sell used books. You’d be surprised at how many of them appear to have never been opened. If it isn’t obvious that it’s used, sure, go ahead.
I also volunteer at a library bookstore, and we’ve had some people in there doing Christmas shopping on a budget.
As for the OP, oh, heck, I’ve done it myself, being careful not to break the binding or smudge pages, and told the recipient that I would or did. 
When the mom mentioned it, that is how it sounded to me. That she was taking real pleasure in reading the books before her sister even though they were meant to be a gift.
You seem to be taking this very personally. I’m sorry if it hit a nerve or something.
My friends and family take it completely for granted that I will read gift books first, and I take it completely for granted that they have.
And…yeah, washing one’s hands is kind of important here!
If your intent is to give a used book as a gift, then by all means read it first. I don’t have any problem with the issue of reading it first - but it’s pretty hard to read a book without making it look and feel read. Even if they washed their hands and removed the dust jacket, I suspect I could still tell if a book had been read by most of the people I know. I would definitely know with a paperback. As the recipient, I wouldn’t be offended, but I’d be thinking “This is a well-preserved used book” and that might not be what the gifter intends.
No, I’m just curious about irrational behavior in general. There must be some sort of internal reasoning process involved, and I’d love to know more about it.
I think it’s tacky to use a gift before you give it.
I wouldn’t do it but I don’t know that I’d get all that upset if my friend read the book first. I wouldn’t do it though.
I’ve received a basket of a dozen or so used books as a gift, probably for the cost of one or two new books. I like literary fiction and it’s not cheap new, so it’s just smart shopping. Why the need for secrecy? Reduce, reuse, recycle, folks… Save a tree!
This.
And this.
We bought books for most of our Christmas presents this year - they’re sitting over there, <—, not getting read by me, because they’re gifts, and not for me to read. I also agree that you can tell when books have been read already, and I would know that I read it already, then passed it off as a new book. If I want to read it, I’ll ask to borrow it or buy my own.
I wouldn’t do it, and I don’t really like it when my wife does it, although it was for her brother, and they have their own relationship from long before I was around, so I didn’t press it. If you want to read the book you’re giving, why can’t you either buy your own copy, or wait until after they’ve read it to borrow their copy?
Maybe you can buy your own copy, but the answer to that is obvious: it is a waste of resources. You don’t use up a book when you read it. That’s why libraries are an okay idea. So why act like you’ve violated the book by reading it? Are only virgin books worth reading?
I wouldn’t do it. It feels tacky to me.
No, but this is about gift giving, not book reading. In general, most people do not give used gifts, even if using them doesn’t use them up.
In my opinion, it’s not about the book, it’s about the fact that it’s a gift. Ultimately, if you give someone a gift, you’re saying that they are worth you sacrificing something for them, usually time and/or money in practice. Giving someone a book I’ve already read isn’t really a gift, unless I particularly intended to read it again soon, it’s just a general part of friendship. It’s the difference between buying someone a pint if they’re short of money, and buying them a bottle of scotch as a present.
In short, it’s not so much about the object itself, but about what you’re actually doing. Sharing something is not the same as giving something. Both are good and worthy things, but have somewhat different meanings.
So why can’t you borrow it after they’ve read it?
That’s right; I can buy you some lovely gift soaps for Christmas - you don’t mind if I take a bath and use them to clean myself before I give them to you, do you? After all, the soaps have many uses left in them. 
Tacky. I like that new book smell and feel. Not cool if someone else screws that up for you.
… which is what my son did. I didn’t think twice about handing it on to him after I’d read my book. I would’ve been miffed if he’d read it first.
Sure, that’s how I’d likely do it, especially since I’m more of a last-minute shopper.
But doesn’t that just potentially inconvenience them? Now maybe they feel rushed to read it, or maybe it doesn’t appeal to them in spite of your best efforts and now you’ve obligated them to read it or pretend to have before lending it to you. It’s meant to be a gift, not a chore. If I did read it first, I’d tell them. What’s the big deal, just some rule for the sake of being a rule?
Buy the book for yourself, read it, and then offer it to your friend.