Webster defines Sanity as "Mentally sound; possessing a rational mind; having the mental faculties in such condition as to be able to anticipate and judge of the effect of one's actions in an ordinary manner."
Sanity also implies that a person does not exhibit any sort of pathology (i.e. A departure or deviation from a normal condition). So, to be sane, one must be "normal," or exhibit a mindset similar to that of his own culture. America has a certain set of cultural norms, and deviation from that will be considered a deviation from sanity. However, that would lead one to ask "What is normal?"
Normal is defined as "According to an established norm, rule, or principle; conformed to a type, standard, or regular form; performing the proper functions; not abnormal; regular; natural; analogical."
So, to be normal/sane, one must be somewhat of a conformist. Conformity seems to be taken as somewhat of a negative term these days, as it seems to imply the departure from individuality. People have such a strong desire to be unlike everyone else, that sometimes that mindset leads to the development of pathologies. And as stated above, a pathology would not be consistent w/ sanity.
So, I guess what I'm getting at is, that I consider "sanity" to be a person's desire to develop and maintain a general cohesiveness w/ his fellow man. A "bond" if you will. People who tend to be introverts and retreatists from society, generally lack what we would consider a "sane" mindset, as they develop or have developed abnormal/deviant behavior.