I may be a bit odd too but with the clothes we were given that were too big to wear straight away (like size 0 jackets given at birth!) I left tags etc and just popped them in the wardrobe for later. Except later never happened for these.
I'm the same now so I don't think that odd. With DS, I was keen to get everything washed in advance but I learnt that no matter how gorgeous some of the gifts were, it just turned out to be the wrong size for the season. Unfortunately because the tags were off & they were washed, I didn't feel I could regift & I also felt they would be more difficult to onsell. When they were gifted, I didn't know then that they would be the wrong size, so by the time I realised it was too late to exchange. I ended up passing most of his things on to my cousin when I found out she was pg with her first. I would have been nice to be able to sell them & get something else for him.

Since learning that lesson, I kept tags on all DD's things until they were appropriate size & season. As it turns out, there are plenty of lovely things that she has outgrown & never worn. Even stuff I bought myself! Some things I have regifted. Others, I'll be looking to sell as soon as I can find time to take pics. I think I'll sell on ebay or gumtree rather than FB though as I know from the MCN buy/sell site that it ends up on friends newsfeeds.

To the original question, I don't think I would be annoyed as others have said - having kids I know it happens! I also hate that expectation put on gifts. Once gifted - it's up to the receiver what happens. I know my mother is one who would get offended at this as she sees it as a reflection on her. Somehow a "it's not quite right for me" translates to "I don't love you and you are a stupid moron" in her mind. So I have lots of things from my mother that sit around unused but I can't get rid of because of the guilt factor. It's just wrong.