Why is it that as soon as someone becomes famous, the first thing that journalists do is remove some letters from their name? Next time why not just leave them in. Calling Lindsay Lohan LiLo or Kevin Federline K-Fed or David Hasselhoff the Hoff doesn't require too much ingenuity and also makes people uncomfortable. David Hasselhoff need not be any closer to us either in body or spirit and thus does not require a terse nickname with which to bring him more familiarity.
Madonna used to be called the Material Girl, which loses points for being self-imposed but is at least a little iconic. Now everyone says Maddy or Mo. Seriously people, her name is only one word long, it does not require any shortening. Some people think Paul McCartney should be called Macca. Really?
Billary for Bill and Hillary Clinton was a good nickname, both for its poetic assonance and the fact that in the nineties it cleverly personifed them as a single political force. Bennifer didn't have the same thematic impetus but it still sounded nice. Brangelina doesn't even sound like a word. TomKat was thought of by one person at Ok! Magazine or something. It looks like the name of a bad website and also they're annoying people to be talking about in the first place.