Yeah, I broke an office chair by leaning back on it. The point of failure was the steel plate that sits under the seat cushion. A cylindrical section is welded onto it, and the upright from the wheel base goes up inside the cylinder. Well, the steel plate, which was about 3 mm thick, just broke, around the outside edge of the cylinder, outside the weld. I was not impressed. Luckily I wasn't hurt.