Ranked in ascending order of frightfulness:
- All your polo ponies get colic on the day before the club championship
- Your Bentley mechanic is away on vacation right when the Mulsanne needs a service
- Left the gold Breitling on the yacht; are forced to wear the oh-so-common steel Rolex to the White House dinner instead
- Your company’s stock drops 2%, causing your net worth to plunge to a paltry $5 billion
And the absolute worst problem any rich man could have:
- You’re married to Wendi Deng.
Further woeful suggestions in Comments.