Sometimes it's a lot more low-key. Your main character may just not like how it makes them an outsider.
Going skiing with your family is fun, you have a good time, and then you come back to school and everyone's talking about their winter break. So-and-so played a video game and you all laugh at their anecdote about a particularly gruesome death, your best friend stayed at their grandmother's and you all nod appropriately about how family is good in small doses. When you talk about a spectacular fall on a black run, you can sort of see the disconnect in their brains. They don't relate to you. You are an outsider. You seem like you're bragging, even though you're just trying to tell a funny story.
Little things build up. You discover your friends are uncomfortable inviting you to their house because it's smaller than yours. They turn down a dinner invitation because they can't afford it, and suddenly you have to constantly question yourself every time you hang out. Would it be appropriate to ask them to spend their money? If you offer to pay for them, it hurts their pride, and creates another rift.
Even if you don't flaunt your wealth, and you're not oblivious to the real world, a coworker might resent you, because you didn't have to work through college.
Your character doesn't need to be angry, they don't need to be angsty, they don't need to be spoiled. They just need to be uncomfortable with the fact that they are more well off than the people around them. Hesitate a second more whenever money comes up, not because they can't afford something, but because they can, and they aren't sure if they should or not.