an internal source of extreme amounts of energy used during times of physical exertion such as sex or rowing
Idiot: Barney, it looks like you are getting a little round around the middle *poke*.
Barney: No, you idiot, that is my fuel tank. It is how I pwn you so hard when it comes to fucking hot girls and on the water!
The Fuel Tank 4 is ultra fast, steamrolling past the competition.