What the F*ck is Common Sense?

I always told my father, "I hate people that have no common sense.  It's annoying!"  But one night, while my family was out to dinner, he posed a question.  He said,
"Well, what really is common sense?"
So I thought about it for a minute, and I realized that i could not produce a definition for "common sense", so I replied with, "well i guess it's like a 'look before you cross the street' kinda thing.  If you don't look before you cross the street, you may get run over."
My dad said to me, "yeah, but a two year old doesn't know this."
So then came the question, "where does common sense come from?"
My answer was, "um, your parents.  If you have a parent that's a total dipshit, then most likely, that's how your kid is gonna be."
So now we get down to the root of it all.  What the fuck is common sense?
Common sense, as described by Merriam-Webster, is defined as beliefs or propositions that most people consider prudent and of sound judgement, without reliance on esoteric knowledge or study or research, but based upon what they see as knowledge held by people "in common". Thus "common sense" (in this view) equates to the knowledge and experience which most people already have, or which the person using the term believes that they do or should have.
So, basically this means that common sense is the shit that you should just know and not have to think about.  We can also refer to some more humorous definitions as defined by urbandictionary.com. 
As defined by user "Metropolitan Gray":

Common Sense:

1) Something the general populous of Earth lacks. 2) The ability to discern what is right and what is wrong. 3) The ability to discern what is intelligent and what is stupid. The blaming of obesity on fast-food restaurants and not on people who should know that fatty food makes you fat. Basically common sense is knowledge that you think others should know, and if they don't then you perceive them as being stupid. Now we come to our next question: who has common sense? My belief is that everyone has some common sense to a certain extent.  Some people may be dumber than others, but each person has at least the tiniest bit of common sense.  For example, everyone know what's right and whats wrong.  Some people just choose to do what is wrong, leading the general public to believe that they lack common sense. Now, we come to our third and final question, "where does common sense come from?"  My opinion is, exactly like i said earlier.  It is a parent's job to instill knowledge into their child's brain.  Part of that is by giving you child common sense.  In other words, if someone is a total idiot, most likely, their kid is going to be too.  Children learn by doing, and also by what they see others doing, and since the parents (or whom ever is raising the child) are the biggest influence on most children, I can come to the conclusion that the parent is the most direct reason for a child/person's lack of common sense.  But you can't put ALL the blame on the parents.  Children have babysitters, teachers, they are also influenced by other children.  I just put most of the blame on the child's parents/guardians because they have the most direct contact with the child. Opinions/comments? <3