Let people know what kind of emotional weather they can expect from you with an appropriate choice of t-shirt. If you're professionally obliged to be perpetually cheerful (or ill-tempered, etc) you can just wear the same thing every day!
You're the CEO of a major bank and the Federal Reserve just gave you a gigantic amount of free money.
You couldn't get your shoelaces the same length on both sides this morning. People better watch out.