Be their sex for the party tonight

"Well," Gayle began, her hand running the length of John's shaft for emphasis, "Me and Terri were planning to liven up the party tonight."
John shivered as the pleasure ran through his body. "And... how does that involve me?" he said slowly.
Gayle ran her other hand along John's cheek, driving him wild. "We were planning to start up a great, big, massive orgy tonight." She said, shocking John.
"Wouldn't that be great?" Piped in Terri, stepping forward and bending over to give John a great view of her tits.
"Y...yeah..." John answered, not thinking straight.
"So what we need, is for you and your girlfriend, Kirsten..."
"Kristen." you correct.
"Kristen. We need you and Kristen to be our sex slaves so we can start the action." Gayle finished.
"WHAT?!? John yelled, surprised.
"Well, it won't be that bad..." Terri said, running her hand down John's chest.
"And what if I say no... or Kristen says no?" he asked.
"Well, John, this may feel good..." she said, stroking the length of his cock once more, "but pleasure can soon change to pain..." she finished, and her grip on his cock tightened to a painful level.
"Youch!" John winced, before Gayle relaxed.
"So, you see that you really have ****. But, if you and Kirsten..."
"Kristen." you correct once more.
"Whatever. If you both agree, then no-one will have to get hurt." Gayle finished. "So what's it going to be, big boy?"
John thought for a moment.