BMW will perpetuate the douche stereotype here at your age. If you want that continue with the M4 purchase. There are many other cars out there that are better choices for many reasons.
As far as why people may be reacting to you one way or how you seem to be perceiving it. Some thoughts...
In general no one here cares about dress code anywhere but a few places. Ex. The Opera. With the right carriage you can go just about anywhere here in jeans and a dress shirt in winter and nice khaki shorts and a decent linen shirt in summer. Those are the formal guidelines if absolute. Everywhere else is just about good with t-shirt, shorts and flip flops.
Your carriage should not be one of arrogance or douche. Education and confidence is ok but do not come off as a know it all. Even if you do know more than who you are speaking with do not embarrass or talk down to them. Leave that for being an internet bully. Instead ask questions that direct them towards knowing exactly what information you seek, even if they have to get it from others. This makes them feel empowered.
Make direct eye contact every once in awhile. This understandably can be difficult for a lot of people. Practice with a close friend who can give you feedback. Keep a healthy posture when needing to assert yourself. Assume a more rounded shoulders posture when needing help from others or to show submission.
When negotiating always try to maintain a few inches of height above the other person. Move your chair up if possible, sit up straight or stand if they are sitting.
Assume the strategy of quiet display of wealth. For men of means this should really be no more than 3 articles on them at anytime. Car always counts as one so carefully consider your choice.
Do you wear an expensive watch or a very functional but you wouldn't care if it broke watch?
Expensive wallet or sunglasses or shoes? Do you wear any jewelry?
Do not talk about money. Period. Outside of a spouse or your accountant. Your financial matters are not anyone's business. Let alone the damn grocery clerks. If people like that assume anything, let them assume. Nod politely, say thank you and have a nice day. They eventually will get the hint. You need to get a bit past what sounds like some internal stigma you seem to have with money.
My best advice is to not buy fancy shit but be investing at a very minimum of 40% of your income so depending on your situation you can think about fully retiring at maybe 50 or earlier. Then just tell everyone to go fuck themselves and blame it on being old like I do.
If you are trolling maybe this will help someone else and a hearty fuck you!