Your goal is to smack a weasels head with a hammer in order to push it back to its hole.
You have to consider, that hitting a weasel with a hammer in the face is not quite a challenge and of course humiliating for the poor animal.
The phrase "Pop! Goes the weasel." in terms of conflict resolution describes the effortless humiliation of another person.
The phrase does not refer to a fight being fair or not.
You could use this phrase to comment a situation in which you owned.
(Well, not because she whacked his weasel but because it was quite effortless, you know.)