DeadlyYellow said:
This.
Or a potato, and leave it near some french people.
Find someone who's got an android phone, and quietly stick it over the little droid logo. Ditto any other competing phone or music player. The more primitive the better in fact. Bonus points if you can get it onto a Nokia 3310 or earlier.
Swap them out for the badge on a VW / BMW / Merc.
Stick onto a card or foil backing, punch a small hole, wear on a chain round your neck as if they were said car badges. Or, make earrings out of them the same way.
Put them on the eyes of a dead relative at an open-casket funeral. If asked, explain they're to pay the ferryman to take them across the Styx, and also to provide them with a complementary iPhone.
Stick over the eyes of a cuddly toy somewhere.
Convince a police officer to stick it over the badge on their hat.
Oh, I dunno. I still actually don't know what to do with the stick-on VW hubcap centre badges that I bought just before having to get rid of my (WC) dub, or the "Sony Mobile" transfer that came with the replacement headunit I put in the same car.
Stick it over the Start button on a Vista or Win7 machine. Like, physically on the screen. Whilst it's running but the owner isn't about / is distracted. See how long it takes before they realise it's not a graphics bug or virus. I know some who wouldn't figure it out even after fully shutting down, removing the power, then plugging back in and restating. Large lulz potential if you pick the right target.