Stupid question: what makes a dog "ugly"?

i know it may seem like a very imprudent question but my curiosity can't help taking over. You know those ugly dog competitions....well makes most dogs ugly? Dogs lok almost identical to dogs of the same breed so how does a dog become/ be born ugly? Is there a specfic condition n dogs that result in facial problems? or are the dogs in the competitions just poor victims in of a freak accident?are they crippled? sick?\