Regifting is when you give a gift that someone gave to you and yes I think it is rude.
Regifting can be hurtful to the person that gave you the present because you don’t know hard that person work to buy the present or what it mean to them.
If you didn’t need the gift you could donate it or give it to your sister, that way someone can still use it. Also you can ask if you can return or exchange the gift.
Regifting is inconsiderate, most people take time and care choosing a perfect present for people to regifting it.