I'm going to tell my friend that he should return the gift he got me.
Can you explain some of the reasons why you want the gift returned?
He'd just better know that I mean it.
If your friend has given you a gift, you should be thankful and appreciative of it, even if it isn't something that you really wanted. Asking your friend to return your gift can be seen as rude and pushy. Even if you don't like the gift that much you should still appreciate the thought and effort that your friend made on your behalf.
WTF. I just want the gift that he gave me returned.
If this was a gift to you, then it is now your property, so you should return it if you really want to.  There is no reason to force your friend to do so, or to tell him so bluntly that it was unwanted.  Just be glad that he did something generous for you, and then move on.