IMHO, some peoples will definetly disagree, somebody who's flashing $100 bills is only doing so to... flash... Show how important they are and how rich they are... Again, this is personal opinion and an opinion is like an asshole, everybody's got one.
Come on guys, isn't it just the power trip of having those $100 bills that make the difference? Hey! I even met peoples who were making a must of always having $100 bills on them, just to show they could have them, even if their bank account was closer to $0 than to $10,000.
Then why carry $100 bills if not to show-off? The only reason left I can see, since most legal stuff worth paying with $100 bills can be paid with plastic, is the person carrying $100 bills who claim not doing it to flash is either lying to me or to herself or, that person is dealing in some illegal business. Who would want to be suspected of doing illegal stuff? It's either this or flashing and either way, IMHO, this is bringing unwanted attention on myself so I don't see why I'd do it and I won't pay somebody with $50 or $100 because I don't want them to be seen like that either.
SPing is almost the only time I'll ever spend over $100 and do so with a person who doesn't accept either debit or credit cards. Why bother with getting $100 bills? $400 is still $400, no matter if it's in $20 or $100! Yes, there are times doing business legally between peoples where cash is a good idea but this is minimal.
Personally, I hate $100 bills. I'm not fond of $50 either. Why? Harder to get them circulating is one reason: find me any clerks in a convenience store who appreciate somebody buying a pack of gum with a $50 or $100...