A One Man Wrecking Crew is just what it sounds like; a single man who wrecks shit.
This term is used when one guy gets into a fight against more than one guy, and deals some serious fucking damage.
The One Man Wrecking Crew could either win or lose; that doesn't matter. It all comes down to how much destruction he dished out.
This can be applied to violence in either reality (a), or even video games (b).
"Holy shit, man! Your face is messed up!"
"You think this is bad, you should see the other guys. I was a One Man Wrecking Crew!"
"My entire team quit but me. I lost, but the score was 39 to 41 before the timer ran out. I was a One Man Wrecking Crew!"
"These four guys jumped me the other day, a bunch of pussy freshmen trying to act tough. What could I do? I felt bad, but I had to either One-Man-Wreck them or let them beat up on me. I chose the former."