At-will only provides protections for specific types of discrimination. They can’t fire you for being part of a federally protected class. For instance, they can’t fire you for being a woman, or for being black, because sex and race are federally protected classes. But “making fun of a dude who drunkenly wrapped himself around a tree” isn’t a protected class, so the firing would be legal in an at-will state.

However, OP can (and should) file for unemployment ASAP. The former employer may try to contest it to get it denied, but that’s just to avoid paying extra on their insurance. If OP appeals the denial, they can submit a reason why they were fired. And as long as it wasn’t for cause (which basically requires something illegal like stealing from the company) then their appeal will be approved and they’ll get unemployment.

But unemployment only begins from the date that you apply. So OP should apply ASAP, so the start date is today. OP should also encourage those other fired employees to do the same. Because fuck that employer, they deserve higher insurance rates and we pay into insurance for a reason. Fucking use it.