"If I am the least knowledgeable person, and a co-worker ignores, despises and almost makes fun of me for your lack of experience, how should I act in order to maintain my dignity but also be humble enough to acknowledge the co-worker's knowledge?"

If you are being all but mocked, humility is not called for, leaving is. There is no excuse for mockery.

"Is it normal to be hired as a junior and just being thrown to the lions, with no help or time to ramp up?"

It is at least not uncommon to take a junior person and throw them at a task that we do not expect you to fully understand out of the gate how to do. It's difficult to do much else; a project is a constantly-moving target, and while I do my best when onboarding someone to find a bug they can handle without having to know the whole system, there's no time to create a "curriculum" or formal training on the system or anything like that... by the time it was created it would already be out of date. So "here's a bug" is the only decent option I have.

However I always make it clear that many questions are expected, and support will be given. Plus, one nice thing about this approach is that it self-tunes... if you hire someone who actually tears through things unexpectedly quickly you aren't sitting there explaining things they find elementary to them.

Failure to provide support is unprofessional and downright bad business. It basically ruins the employee not being supported, and few people are so blessed with "headcount" that they can afford to be hiring people, then just leaving them to rot.

"Do all star/ninja/rock-star software developers have rotten attitudes?"

Ha! Probably a question of definition more than anything else. Some people use the term pejoratively and do include "bad attitude" or "extreme short term focus" in the definition. But I'll modify your question slightly to "good programmers", and no, being really good at programming does not require "rotten attitudes" and if you look at those who rise to heroic levels, they're generally known by their peers as very sympathetic and ready to explain things to anybody.

So far, it sounds like you've described a really hostile environment, because even if you are not really up to the job, the experience you are receiving is incorrect. You should not be getting mocked and psychologically run down by your coworkers. You might be getting taken aside by a manager, put on a performance plan, etc., and that sure as hell doesn't feel good, but it's still of a different nature than what sounds like being run through high school again.

Only you can really judge whether you're actually able to keep up. I'm not going to blow smoke up your ass and say everybody is really, ultimately suited for every job if they just try hard enough. That's elementary school lies-for-children, not reality. You could be in over your head, but making that decision requires more information than you could possibly stuff into a text post. The only two things I can say are 1. Yes, that is a possibility, but, 2. Don't measure yourself against the other people who have been there a long time, and CERTAINLY don't measure yourself against the swaggering personas they may be projecting! Measure yourself against the tasks, whether you can complete them, and whether the solutions are good enough to ship (as opposed to abstractly perfect). And, likewise, measure them against their tasks, whether they complete them, and whether their solutions are any good! (It's usually a lot easier to recognize good code than write it.) See if the swagger is really justified, or if they're just swaggering because they are the only ones capable of navigating their own mess. If you're closing bugs on a reasonable schedule, and they're staying closed when QA tests them, you're at least keeping up. Also consider the difficulty of the tasks... if a "fix the font" bug turns into a multi-week endeavor because the code is just crap, well, maybe this job isn't worth fighting for anyhow. (No programming job is perfect or easy but some are worse than others for no good reason.)

Ultimately, you can't get a yea or nay answer from anything anybody says here, so one last bit of meta-advice... after you read this, just sleep on it for a day or two before coming to any decisions of any kind. Let your subconscious chew on this too.

(Also, I post even though many already have because I see few people are directly addressing your very reasonable questions.)