I have a niece who, for reasons beyond the control of either of us, I did not know very well. I bought her gifts using her age and sex as a guideline. So, Barbies. Eventually, I learned that she just wasn't a Barbie girl. Simple communication could have prevented the whole situation, but that's beside my point. She got unwanted and unneeded gifts. What should she have done with them? Kept them forever? Threw them at me?
Regift like you have some sense, of course. Don't open it and blurt out "I don't want this." Don't turn around and hand it to Aunt Martha right in front of the giver. But by all means, if I give you something you can't or won't use, pass it on. Thank me for the thought, take it home (or wait til I leave) and wrap it up pretty to give Aunt Martha at her birthday. Donate it to the charity of your choice,even.
The best course of action is to know what the receiver wants, of course. I love the idea of registering for gifts when you marry or have a baby. Kids write letters to Santa. If you're close enough to them, you don't even need a list. Items will jump off the shelves and scream their names at you.
Anyway, I have no problem with and even encourage regifting done well. I'd much rather see Aunt Martha with it, if she'd love it and you don't. If I get rich, I promise not to cut you out of my will for it. Unless you did throw it at me.
