'Average' means 'in the middle' or 'not extreme', and 'Joe' is a common male name. So 'average Joe' refers to a man who is not extremely different from everyone else.
There are a few different kinds of Joe's:
1) The Cocky Joe- As mentioned above, these individuals just know everything. They have all that new shit too. If a Worthy fan of Hip-Hop trys to converse with a Joe, there is no chance. Simply because the Cocky Joe is too busy yapping about what they know instead of listening for once.
2) The Fake Joe- These Joes are just trying to do what is cool. If you show a Fake Joe a Dope ass album (ex: Get your mind correct by Paul Wall & Chamillionaire) that requires more listening than just hearing the beat, they will not think much of it. But if you hear back from them in a week, they will tell you how dope such a cd really is (but not even truly knowing about it).
3) The Go With The Flow Joe - These Joe's play it smooth. With their ego of rap knowledge on the line, they have to agree that they have heard everything that you present them with. Whether I show them the new SwishaHouse mixtape, G-Unit Radio, or the LL Cool J, they have just heard it all (even though they really havent) and they know more than you.
Even though there are a few different kinds of Joes, in the end they are all the same, and if you dont like to deal with bullshit, dont deal with the Joes, its that simple....and if you dont understand what I just told you, you are a Joe.
"Those Average Joes piss me off so bad, Fuck Em"-Millah