I'm not going to say these are for millionaires. But there are definitely things I think to myself these are silly to spend money on, regardless of net worth.
1) Most things for pets. You know the excess toys, fancy leashes, even dog sweaters, canned food for healthy pets who don't need canned food. Your pet DOESN'T CARE!
2) People who order multiple drinks at a bar where it is SO expensive. Or going out/take out or drive through multiple times a week. It should be a treat, not a normal routine.
3) Bottled water. It's personal pet peeve of mine. There's nothing wrong with the tap water! Bring your own bottle with you!
4) Car washes, unless you're Walter White. (Though I have agreed to take my youngest to one of those drive-in car washes, someday).
5) Spending a lot on a car, double if you have to lease or get a loan for it. I just don't get the huge opportunity cost. People spending 40K on a truck or SUV literally blows my mind. I mean, that's a downpayment on a house. Or put that money in the stock market, walk away, and in 20 years you'll have close to150K.
I guess my pet peeve is that alot of Americans are aspirational. They WANT to do or buy the things that millionaires do, even if they can't afford it so saying this is for millionaires sounds both privileged and snobby and may backfire. It might be better for him to frame it as, hey I'm a millionaire, and even with all my money I think it's silly to spend money on X, or Smart people, smart people with money game the system by NOT doing what the majority does.