I think, as a society, we've become too obsessed with psychiatric diagnoses if we start calling our personal idiosyncrasies some form of mental or personality disorder.
It really depends. If you were to say that we were focused on taking medication to treat everything that we are diagnosed with then I agree. However, the thing that defines a mental disorder is being maladaptive (harmful/interrupting life).
If I were to have a habit of constantly washing my hands would I have a mental disorder? Yes and no. Yes in the fact that I am showing obsessive-compulsive behavior, but also no as long as I don't end up washing my hands to the extent that they start bleeding. A lot of people also meet the criteria for suffering from unipolar (major) depression, but it depends on how long the depression lasts to actually need treatment for it. Unfortunately, we have people that are depressed for three days, go to a psychiatrist (usually only prescribe medication) and suddenly think they are "cured" which leads to more of a problem later on.
Does having psychopathic tendencies (clinically known as antisocial tendencies) mean that you are a psychopath (antisocial personality disorder is the clinical term)? Absolutely not, people can show tendencies but this does not always mean that they will be diagnosed as psychopaths. Similarly, just because a person that plays GTA and constantly kills civilians does not mean that they are psychopaths. It can be considered worrisome, but we can not show a cause/effect between video game violence and real life violence.
We can show a correlation, but that's a different can of worms that is easily construed by people not educated in statistics.
If you just look hard enough you can find a mental disorder in every person on this planet.
Yes, but that does not necessarily mean that they actually have that disorder. There's an interesting book by Ethan Waters entitled Crazy Like Us about that subject.