Now there's an interesting theory .....
Does the inability to kick someone up the bum foment an unhealthy fascination with guns?
I would have spelt that as "ferment" but the dictionary agrees with you. Well done.
There is sense in your theory also. If you can't outlet your rage through arse kicking, it will manifest itself through other mediums. I assume he chose to use a gun, because in a real fight she'd probably win. Knocked him on his arse.

