I'm NOT the OP, but I went ahead and did his work for him. I went through and counted each poster 1 single time until I got up to the 50th unique poster. That poster is "knotfan123". Sadly, I was unique poster #52
Feel free to check my work as I may have made a mistake or two(hopefully two so I'm the winner lol).
And even if the OP meant the 50th post, he should go with the 50th poster anyway just because of the massive spam that went on.
excluding the OP, the 50th unique poster is monkeydjesus, including the OP, it's KansasFF. excluding the OP, the 50th post is by The Keyboard Wizard, including the OP, it's by digital83.