An acquaintance of mine - a manager high up the food chain of an international company - recently approached me for advice in a delicate situation between him and his boss. As their business has done well, high provisions were paid out for the last year. My acquaintance decided to buy a brand new electric car of a well known manufacturer for just under 6 figures.
He was having a polite but rather formal relationship with his boss until now. According to him that changed beginning the first day he drove into the company's parking lot with his new 'toy'.
While the car attracted considerable attention from colleagues and employees in general, his boss didn't even mention anything or ask him about it. The boss's attitude towards him changed from formal/polite to being passive aggressive, either by lecturing him in front of others in the weekly meeting or ignoring him when asked about certain directives regarding customer relations.
My acquaintance suspects that the sudden change of behaviour is due to some compensation mechanism of the boss since he (the boss) is accustomed to having not just the biggest, but also the most expensive, (private) car by far.
He doesn't know if he should openly approach him in a private talk after office hours or if he should just ignore the change and hope that the boss eventually settles down and their relation will become as it was prevously before he bought the new car.
Since I didn't have any practical advice for him since I haven't been in such a situation I thought I would ask here. What is a good way to handle this conflict in an effective and constructive manner?