I'm just nitpicking as usual, but I'm really curious what the right usage of commas is when used in a series. I go with 'A, B, C, and D.' I'm not sure if this is the correct way to use it, but I must at some point in my life have been taught to do this because I have been using it that way so diligently (even though I have no idea where or who taught me that, way back in school most likely).
However, 90% of the time, I see people leave out the comma before the conjunction - A, B, C and D. All major newspapers, most books that I read use it this way. And just when I start to think I'm wrong in using the comma before the conjunction, I see someone using it the same way I do.
I'm too lazy to research. And besides, I promised myself I wouldn't waste time researching anything to do with grammar :P But I'm still curious. I know it's a trivial issue, every time I mention this, my friends shake their heads and give me this exasperated little look. But every time I see a sentence with the missing (according to me) comma, it screams out at me. I want to make sure I'm not bothered for the wrong reason.
So A,B, and C or A, B and C - what exactly is the right usage here?