Isn't it obvious?

John grinned.

"Well, seeing as you're halfway naked...we might as well fuck."

Jennifer shrugged. "Fine with me."

As she bent over, John shucked his pants, gripped her hips, and prepared to ram it in...

Whereupon Lacey entered the room, asking, "Hey, what's taking so long?"

She caught the tableau and, without missing a beat said.

"Hey, can I join in?"