Twilight and Rainbow Dash both did favors for Spike once.
The results both disgusted and amused each other, but they unknowingly started something beyond their control.
Now Pinkie wants in on the prank.
Nopony out-pranks Pinkie Pie.

Obvious sequel to Twilight's Palace is Covered With Semen.
I got permission from both Majin Syeekoh and AndThatsTerrible.
Now with a live reading. You have been warned.
Also has a sequel Black Pony's Twilight's Kingdom is smothered in semen. Again, you have been warned.
I regret nothing.