Stay Out of the Bathroom (Gooflumps #2 1/2)
No one--not his parents and certainly not his kid sister--can make Joe Kohler put down the toilet seat.  Not now.  Not ever.  But then the bully of the bowl meets his match.  First the toilet refuses to flush.  Then a stomach virus brings Joe head to head with the beast, and the seat comes slamming down. Joe escapes being beheaded in the bathroom, but he realizes too late that the toilet isn't a toilet after all.  By that time, he's been taken aboard an alien spaceship!