For me TODO is more literal, reserved for things that must be done. So, I use SMELL if it's unsane. If it's somewhat broken, I use BUG, and file a low priority

For me TODO is more literal, reserved for things that must be done. So, I use SMELL if it's unsane. If it's somewhat broken, I use BUG, and file a low priority issue. For both, I put long explanations, in the code, for the future reader.