Alright, try to imagine this:

Ceasar got hard staring at some of the beautiful mares at the gala (with his monocle :3). Dash turned her wings around and started flapping furiously while jogging backwards. Her hooves hit a patch of liquid caused by a spilled drink, and she began to pick up some serious speed backwards. While he wasn’t paying attention, Rainbow rapidly flew in and slid backwards under him. Her dress caught on his chest and underbelly and got hiked up as she moved in. And thus, in the blink of an eye, Dash impaled herself on a completely unsuspecting Ceasar. At that exact moment this picture was taken. That explains the facial expressions :3