Yoiks. How can you knock off your own toe?
Maybe Slash needs a new moniker: Like Joe Btzfrxk? Or something else with its own little hovering rain cloud...
Oh, that happens when you come around the corner too fast, cut it a bit too close, and ram your foot -- toes first -- sideways across the corner where the baseboards meet.
Other candidates are squarish table legs, and the lower corners of filing cabinets, book Cass, and other similar furnishings.
The odd engine block resting on the floor in the garage will do in a pinch.
Done properly the lateral momentum focused at the corner's edge is sufficient to deform one or more toes sideways to the failure point of the underlying skeletal structure. While this impact, alone, will not likely result in severance of the digit, the likelihood of complete severance increases proportionally with the sharpness of the impacted corner, and the angle of approach, and the pain will be every bit as severe as if severance had occurred.
Also, it is widely agreed that, unless the injury is to the big toe, recovery from complete severance is actually more rapid, and less painful than recovery from breakage due to this kind of blunt force trauma. Note that advocacy for whatever course of action this may lead you to pursue is expressly disclaimed hereby.