If I have an idea that I present and to someone or a group at a school function, and they take the idea directly from our meeting and sell it, can I sue? Or do I literally have ZERO protection without a patent?
DonQuiKong's comment "you should be asking if you can win a lawsuit" is quite salient, as Intellectual Property litigation, and patent litigation in general, is extremely expensive. (This was a reason "patent trolls" were able to extort companies to the average tune of $2 million dollars--cheaper than going to court.)
One means of protection is to file a provisional patent application. Not everyone agrees on the wisdom of self-filing, but I know experienced patent attorneys who are adamant an attorney is not strictly required for a provisional, so long as the invention is fully and rigorously described.
The other route is to have the person or people sign a non-disclosure agreement. This allows you to disclose in a manner that does not constitute public disclosure which could render your invention ineligible, depending on the rules for the region(s) you may be planning to file in. (See also: At What Point Do Conversations Become Prior Art?)
If you are not planning to file a patent application yourself, then public disclosure may be a way to invalidate a subsequent filing of your invention by another party, but the problem is, the patent examiners may not become aware of the public disclosure, and the application could still receive a grant. In that case, you'd have to challenge in court, which, again, could be ruinously expensive.