Simple straight forward conversation, just like you've had here (only a little more polite than you've worded here if you value the friendship).
You're not his parent, and he won't listen to you anyways, so I'd leave his financial decissions out of it, make it about yours.
Tell him you're happy with your truck, you don't have a great desire for expensive cars and are not interested in getting in a lot of debt for something you don't really care about. Same thing for anything else that applies (you said that was one example, so if he likes expensive clothes, facy dinners, whatever else - same deal. You're happy with what you have and would rather have the money for other things).
If he pesters you after that tell him you've discussed it, and if he's your friend beyomd it being safe, reliable and affordable he shouldn't care what kind of car you drive (etc same deal for other stuff). If he doesn't listen then he's not really your friend and better to find some folks who are as happy to roll around with you in a used F-150 as they are a new S500. You don't have to act like the guy is dead to you, everyone has flaws and there are worse than liking fancy cars, but don't entertain the conversation further.
(post is archived)