What does the metaphor fishing with dynamite mean?

Answer 1

It means you cannot fail. Imagine a guy in a lake with a rod and one line, how much easier would it to drop a stick of TNT in the lake and scoop the fishies up from the surface? Or another way to look at it; if Brad Pitt walked into a bar full of single women, that boy would be fishing with dynamite....

Answer 2

Dynamite fishing is the practice of using explosives to stun or kill schools of fish for easy collection. It is considered illegal because this can destroy the coral reefs where most marine animals live.