A 4-foot Batman Batarang. I wonder if you could hang glide on that thing. I wonder if it would make a good frisbee. Or, at 4-1/2 pounds, a good World's Strongest Man chucking event.
According to ThinkGeek, the answer is, "None of the above." They do not recommend throwing or otherwise letting the giant Batarang loose in the air at all. It is not a toy, but display piece. It is intended for wall mounting and mancave decorating only.
At least if you're the rules-following type.
The Big Ol' version of Batman's Batarang is made of foam rubber (a little less dangerous than steel, at least!) and measures 47" across x 17" up and down. While a wicked cool and thoughtful superhero gift that definitely proves you love someone, the giant Batarang is not recommended for anyone under 15.