>Has anyone ever become maybe overly assertive when a boss blames you for something because of their own bad management?
Yes and it's frustrating as hell and it also kind of goes with the territory. I've also been on the other end where I was the boss and stupid employees fucked it up and tried to turn it around on me and that's pretty fucking frustrating too.
So, general suggestions
1) Focus on the immediate problem and getting that solved. E.g. you told boss last week that you were running low on plastic forks and he said "I think we'll be fine, stop worrying about it" and then this week it's "user what the fuck, how did you fuck this up so royally that there are no fucking forks left, you idiot?" Try to resist the temptation to take the bait "Well, I'm sorry we ar in this situation and right now I'm working on tracking down some more plastic forks"
2) From now on, going forward, politely but firmly focus on preventing it next time around. So, next month, when you are concerned about running out of forks, then, well, send an email, and also be a little more forceful about saying "Hey Boss, don't mean to bug you about this, but I'm concerned about running out of forks again, so, if you want I can order them, but I need your password, but I just want to make sure we are covered when it comes to forks.
Next, generally take a look at the boss and evaluate. Is boss generally a good guy, but he was a dick about that particular situation with the forks. Well, then, I say, hey, look, nobody's perfect, let's let it go.
OTOH is boss the kind of guy who is constantly pulling this shit -- you want to be ESPECIALLY careful to see how he treats other people as well. Because if this is a habit, then you just need to get the fuck out asap. The chances that you are going to (1) convince him he is in the wrong or (2) get his boss to do something about it is basically 0. Not saying it never happens but it is FAR more likely that it blows back on you. Just GTFO.