How to get rid of a dot of hard nail glue from my iPhone 5?

It's on the menu button though its not that visible to other people, it irks me knowing that its there! I already tried acetone, rubbing it with a cotton pad and nothing! It's still there.

If you know the name of the glue manufacturer then go on their website and ask them for a solvent, but be sure to mention that it is stuck to plastic or you may end up with no phone key at all.