At the end of the movie, Bender is outside and is putting in the diamond earring Claire gave him. In the first scene when they are all together at the tables, notice that Bender already has the earring in, long before it was given to him. I believe if you look closely thru-out the movie, it appears and disappears.
If you watch closely, you see him take OUT an earring to put that one IN! I assume the one he took out was a fake diamond that he had the whole time, because Claire is never seen without hers.
It doesn't look like a diamond to me. It looks like it's something flat against his earlobe. Also, if it is a fake or different diamond, it's much bigger than the one she gave him at the end. It does seem to disappear, but I did notice that if his head was facing a certain way, it didn't look like it was there. When he would move his head just a little bit, you could clearly see the light shining on it. With this being said, I did notice that, at least at the end, it wasn't in his ear.