1.
When a man is having sex with a woman from behind, he grips her waist,lifts his feet and starts kicking her in the breasts.

2.
When the seat is removed from a bicycle leaving only the seatpost. So when you ride the bike the seatpost goes up your rectum or vagina.

3.
When a man is having sex with a woman from behind in the doggy position, there is another woman riding the woman as if on a bike holding her braids like handle bars and making a pedaling motion with her feet, and massaging herself.