I guess this must be archaic, but then much of my vocabulary is. To poormouth is to talk and complain as though you are poor, particularly when you really aren't. College kids with a constant supply of cash from Mom and Dad are frequent poormouthers, but nearly everybody does it once in a while. It's only reprehensible when it's particularly egregious--whining that you couldn't afford first class to Japan for winter break, just business class.

Unlike badmouth, you can't poormouth someone else.