The fifth one

Horny: "I'd like to chat with the fourth one."

callmeSir: "Wonderful, I'll let her know."

A moment later, callmeSir posted an invitation to a private chat room. You click it, and enter.

Horny: "Hello."

Merry_Minx: "Howdy Horny. I'm Merry Minx, you can call me Merry, or Minx. Or slut, whore, bitch, cunt, anything like that."

Horny: "Haha, I'll just go with Minx for now, but we'll see about that later ;)"

Merry_Minx: "Not too much later, I hope! I was hoping we could start soon, I'm already horny, and I'm not the most patient girl."

Merry_Minx: "Also, I was thinking you could handle the ideas for this, Horny. I don't have any at the moment, and I think it'd be fun for your first time."

Horny: "Well... I did think of something."