What exactly is bad design? Because design is so subjective, it's one of those questions where you have to ask yourself, "When am I doing a bad design? When is a design that I'm doing just not favorable for the audience or the company? When do I need to get better?"
I believe every single question that you ask yourself in regards to getting better is the right one, whether it's learning new skills and new trades by constantly staying abreast of what's going on in the blogs or with other people that are earning awards or different magazines that you can look at like "How," "Communication Arts," is really just seeing how your work lines up in terms of talent. Also I believe a good answer for the question of what is bad design is simply bad communication. If you're not able to communicate effectively what it is you're trying to design, then it's not necessarily a bad design, but maybe your design has just possibly failed.
There can be a time, I guess, when we become so ingrained into everything that we're doing, all the designs that you have to put out daily, everything, that all the demands from clients and from your peers and from different outlets, but the main thing to remember is basically what can I do to answer the question that the client is asking or wants answered. Or what can I do to understand the client better? Or what can I do to really make sure that my design is answering the question? Bad design is probably an outdated term, but it's good to continually ask yourself the question that your clients may ask you or that you may not get asked but that may make you a better designer.