There's an anarchist theory of economic monkey wrenching that pretty much defaults to do as much damage as quickly as possible, then retreat. So get as many big corporate credit cards as possible, max them out (at corporate stores, not small businesses because small business is a form of anarchy), redistribute/move on, never pay up. (I'm not saying I approve or advise, but I'm not an anarchist. Just an amiable Democratic Socialist with odd friends. I also don't know anyone who had ever done it, or at least, anyone who admitted to it. It's also how most ID fraud works.)
That no bounce, no overdraft, no minimum is a point of failure. Hit the system fast and hard and it probably quakes. I don't know what WM's internal books look like, but if they're like pretty much every other corporation, most of their wealth is close to imaginary. Corps have come down with relatively minor wounds to strategic targets before -- Enron, Arthur Anderson, Washington Mutual...
The thing is, it could happen without any intentional organization, just the economics of being poor and having a lot of poor people who are all unbanked, who all have cash flow problems, who use a single vendor for most of their consumption -- and that describes WM. I'd bet February looks bad, since February is the hardest month if you're poor -- 24 fewer working hours (assuming an 8 hour work day), cold, so higher electric/gas/oil bills, and the rent stays the same.
They're already in a less than excellent situation, given that sales are flat or declining, and they've annoyed almost everyone.