Don't we all have that one mysteriously wealthy friend? The guy or gal who claims they work in finance or film or art but is somehow never in the office and always in St. Barths or a private members' club in London? You have a sneaking suspicion that they're secretly royalty and/or a massive drug dealer. But when it comes to gifting them, well, that's a bit more difficult. So, what do you buy a one-percenter in whose good graces you'd like to remain?