Can You Venmo Me?
No one likes a cheapskate, which is why you shouldn’t keep tabs on friends and family. It’s one thing if you lend them a large amount of money, but if you cover the bill for them every once in a while – especially if you can afford it – you shouldn’t make a big deal of it, and you shouldn’t ask them to pay you back.

Apparently, this person didn’t get this memo. He actually asked his mother-in-law to pay him back for a $4 soda. Even if he wasn’t filthy rich, as the OP claims, that would still be a rude and tasteless thing to do. Knowing that his annual income is over $500000 only makes it that much worse.