In the pantheon of comedy history, few bits are as polarizing as Gallagher’s Sledge-o-Matic. The late prop comedian, whose legal name was Leo Gallagher, filled his stand-up performances with wordplay and demonstrations of his elaborate homemade gadgets. But he closed every show with a tried-and-true crowd pleaser that came to define his entire life. He placed a watermelon on a stool, performed a monologue that mocked infomercials for kitchen products, and then smashed the melon with a sledgehammer.

The audiences who willingly bought tickets (and donned the required plastic ponchos to sit in the front row) were always amused by the gag. But to outsiders, it was the height of hackery. Stand-up comedy is a time honored art form that can be used to package eloquent thoughts about human society in a way that entertains audiences and relieved cultural tension. In the eyes of its purists, relying on props...