A way to describe someone physically built in a way similar to a fire hydrant, such people are usually a bit shorter, yet solidly built and wide in the shoulders, but not fat. If they are fat they become a tank. Such people usually have good balance, thick necks, a low centre of gravity, and strong momentum behind their punches, and are usually deceptively strong, as seen in MMA fighters such as Matt Hughes and Sean Sherk.
fire hydrant: multiple meanings;
a) to use a penis enlarging pump to make your penis turn large,swollen and red to resemble a fire hydrant.
b) peeing on a red headed girl
a fire hydrant is an inside joke used between my friends.... meaning when a fugly guy sees a hot woman (us) and gets the urge to come and fuck us getting a boner.