When one partner lays reluctantly on his/her stomach and is then penetrated in the anus by their partner. Said partner has their back haunched for maximum insertion-giving the appearance of the shell.
common term for a person who shows lots of anger/grumpiness. When you perceive an angry person complaining or ranting, usually "Grumpy Cannon" is said to annoy/aggrivate them.
The term comes from a Megaman type game, as the thought is that if you beat the commonly angry person, you will inherit their grumpy cannon.