'pretend that the suggestion is bad' - do you listen to yourself? If you can't conceive that your suggestion may BE bad, then the problem is almost certainly you. Either in the way you approach things, or that your suggestions ARE bad.
You are not the only smart person on the internet. Statistically, you probably aren't any nearer the smartest than I am.
If you've been using a package for a couple of weeks you might have some suggestions. If you act like you can't possibly be wrong, then your attitude alone will make the old timers ignore you.
Perfectionism is the enemy of actually getting shit done. Small improvements that make me re-learn how to do things are a big time suck in the near term. You know, when I have to get shit done. Even if the change is long-term beneficial, the amount of time lost right now is probably not worth it.
Asking questions generally gets a far better response than 'you should change this!' comments. Asking why it's done like X instead of Y indicates a willingness to understand. And frankly in many cases there is (or was) some good reason that things were done a given way. Asking questions can get to the bottom of that, and in some cases make it easy to show that it should be changed (because the original reason is gone).
Code talks, bullshit walks. If it's open source and you don't like how it works, submit a change set. It may still get rejected, but no one will question your willingness to make things better. Just your judgement about what 'better' might mean.