Enormous

 Originally, I'd thought the best part of going to the swap spa with my girlfriend was that I'd have her enormous tits for the afternoon and be able to fondle them as much as I wanted. Admittedly, that part was pretty good. It was weird the way my attraction for my new body played out, making my nipples hard, my breasts sensitive, my pussy gushing. The first time I came I was in the hot tub just squeezing my tits when the feeling overwhelmed me and I shuddered, letting out a cute little squeak as I came.
A swapped guy saw what I was doing, which led to the best part of swap spa: being plugged from behind as my girlfriend's tits swung on my chest at every thrust. I didn't know how horny I was or how good it would feel getting my pussy pounded until the stranger was deep inside of me, gripping my hips and thrusting, the sound of our groins meeting a loud slap in the echoey room, soon joined by my girlfriend's cries of pleasure spilling from my borrowed lips.
The worst part of swap spa was pretending none of that happened so that we could return.

 A mother and son accidentally swap bodies and have to learn to understand each other in order to swap back in Freaking Friday, available on Body Swap Stories or Smashwords.