Conan O'Brien!
I have suspected this one for quite some time. But I didn't have the proof to back up my claim - until now! I could tell the front hairline was receding, so it seemed funny to me that despite the receding hair line Conan's hair seemed to get thicker by the day. It looked fake - but then again Conan's hair always kind of did. Take a look:
The bald spot is exposed! And just to put icing on the cake (and because this photo cracks me up):