They have it all backward in the Farce of the Century between Floyd Mayweather and Conor McGregor.

Clearly, after the first of their joint gum-beating sessions Tuesday in Los Angeles, promoters should charge for the promotional appearances while airing the fight for free.

The profane insults and the posturing that normally can be enjoyed only in your better prison exercise yards are bound to be more entertaining than the Aug. 26 fight itself.

While McGregor will strain to land a legitimate hand upon even a 40-year-old Mayweather in the ring, the Irishman is a force to be reckoned with on the dais.

Having read the report that Mayweather needs the August payday to meet his tax bill from his last megafight in 2015, against Manny Pacquiao, McGregor was quick to seize upon his opponent’s weakness Tuesday.

“He’s in an (expletive) track suit. He can’t even afford a suit anymore,” McGregor howled.

From that track suit, Mayweather later pulled a check he said was for $100 million that he just hadn’t gotten around to cashing yet. He seemed so proud that all that money was collecting lint, but no interest. Perhaps he should do something else with that before the IRS takes his fillings.

Hey, wait, I just wrote a check to myself for $150 million, and I feel like a Vanderbilt. Wanna see it?

Back to Tuesday, both men promised a knockout – claims that contain the sulphurous odor of electioneering. Mayweather, the defensive specialist, hasn’t managed a KO since 2011, seven fights ago. And McGregor, the MMA guy who can’t kick or wrestle or roll around on the floor like a human Roomba, is working without a majority of his arsenal in this one.

He is, to use his own words, competing under a “limited set of rules that makes this half a fight, a quarter of a fight.” And I think McGregor’s grossly overestimating this fight’s value.

There never has been a compelling competitive reason to throw these two together in the ring. They come from different worlds – and it just so happens that McGregor’s is the one with the audience now. This is some weird sporting genetic experiment gone horribly wrong.

But at least there is the build-up, which still promises some of the charm of a short film by Quentin Tarantino.

I would rather take a $100 bill and cast it into the Chattahoochee than donate it to the Mayweather-McGregor pay-per-view. You have the author of this decade’s most boring fights, years past his prime, versus a wild-eyed MMA crossover whose frustrations in the ring may well bubble over and make the Mike Tyson ear-bite look like a Shakespearean sonnet. It can’t end well.

But I’d pay a buck and a quarter for their next promotional appearance, if only to see to what depths they may descend.