'tot he party' was ZeaLitY, one of our main mods, and one of his typos, if I remember correctly. It just sort of stuck. I guess. But if you look on the second page of this topic, you see that Z says 'Welcome tot he party.' Then, two posts down, cupn00dles, around when I first joined, quotes him and says, 'You know you can stop writing that if you're not comfortable with it, right? Nobody will blame you, I promise.' (god, I'm never going to get used to this new keyboard.
And if you look further, you see either my first or second post.
I was completely different then.