For the third time in a row, he'd found himself on vacation, in a scenic place that was perfect for motorcycling, without a motorcycle and without any way to rent one.
On a whim, he checked the local Craigslist to see if there were any used motorcycles for sale. There were, but cost close to $1,000.
That led to an epiphany: The country is full of motorcycles that aren't being ridden, and might be full of riders like him who wanted to rent them.
The result is Twisted Road, Rothboard's peer-to-peer bike rental service, which the entrepreneur is calling "the Airbnb of motorcycles."
Some riding enthusiasts are applauding. But insurance experts are raising questions, as they have about Airbnb and other sharing startups, about liability.
Launched late last year in Texas, the service is now nationwide, with a network of around 400 motorcycles and more than 5,000 registered users in 40 U.S. states, including Alaska and Hawaii. A large number of users live in California, where warm, dry weather allows for year-round motorcycling.
Using the Twisted Road online platform, interested riders peruse ads featuring photos, specifications and details on the motorcycles and their owners. Bikes typically rent for $75 to $150 a day, and may include other services, such as pickup and dropoff, or the loan of a jacket and helmet.
"We're connecting the owner with six bikes in the garage with the rider who's traveling and really wants to ride," Rothbard said. "We're offering people an experience they can't have any other way."
Owners are protected by a clause that requires all renters to be bike owners, and active riders, who carry their own motorcycle insurance.
For hosting the exchange, Twisted Road takes 30 percent of the transaction cost. For an extra fee, the company will offer renters roadside assistance insurance and other services.
Rothbard, 46, has a business background, and has done executive stints with Brunswick Billiards, Baker Furniture and Pyrex parent company World Kitchen. He came to motorcycling only three years ago, but took to it at once.
Among his first tasks in building the Twisted Road idea into a company was polling. Rothbard asked hundreds of bike riders and owners how they felt about renting used motorcycles, and how they felt about letting someone rent theirs.
"About 85 percent said they would not put their bikes up for rent, and 70 percent said they wouldn't rent someone else's bike," Rothbard said. "But that meant 15 percent of bike owners would be willing to rent out their bikes, and 30 percent of bike riders would consider renting."
Those are actually high numbers, Rothbard said, citing studies that have shown Airbnb penetration in America at about 1 percent of the U.S. housing market.
"Even if my numbers are 15 times overstated, I'd still be at Airbnb level," Rothbard said. "And that would be a success."
Brandon Desy of San Antonio twice rented his 2012 Aprilia Tuono, for $105 a day, to renters who treated the motorcycle respectfully and returned it in good shape. Encouraged by the program, Desy himself rented a Honda CBR1000, for $150, when he was on vacation in Austin, Texas.
"I used it for commuting and for fun," Desy said. "It allowed me to test a bike that I hadn't ridden before and to ride some new roads I'd never ridden."
Desy's experience inspired two friends, who'd initially said they'd never rent their bikes to strangers. After Desy's two rentals, his friends both listed their motorcycles on the Twisted Road site, Desy said.
The service is similar to what's already being offered, for cars only, by San Francisco's Turo and GetAround. Using those car-sharing services, registered users pay for short-term rentals of privately owned vehicles.
It's also similar to a peer-to-peer motorcycle sharing service called Riders Share, whose founding officer believes Rothbard and Twisted Road are courting disaster.
Los Angeles-based Riders Share, founded a year earlier than Twisted Road, offers peer-to-peer bike rentals nationwide on the same short-term basis. Bikes typically rent for about the same rates as Twisted Road's. The company has a similar number of bikes in its network and a similar origin story.
But Riders Share's pitch differs from Rothbard's in one essential point: Riders Share carries its own insurance. Renters, who must be legal licensed riders, are required to buy the Riders Share insurance before they rent a motorcycle.
Several years ago Riders Share co-founder Guillermo Cornejo destroyed his motorcycle in a high-speed crash. After recovering, he wanted to get back into biking, but his medical bills made it impossible for him to buy a new bike.
When he looked into renting a motorcycle instead, he found only Harley-Davidsons were available, and only through Los Angeles-based Eagle Rider. He didn't want to rent a Harley, and didn't want to pay Eagle Rider rates, but that was the only rental service offered.
Cornejo, who said his business hosted 300 rental days in 2017 and will do about $800,000 in rentals this year, said he worries that Twisted Road is skirting the law by sponsoring transactions that might not be covered by insurance.
Most motorcycle insurance policies, he said, might cover the loan of a motorcycle to a friend, but expressly do not cover any commercial transaction between the owner and a renter.
Cornejo said he believes Twisted Road is misleading renters and owners by suggesting their policies cover the transactions, and worries about the effect of a bad incident on the nascent peer-to-peer motorcycle business.
"I'm afraid they're going to make all of us look bad if someone rents a bike thinking their insurance covers it, when it doesn't," he said. "Suppose someone is killed, or kills someone else? That's going to look terrible for everyone."
"If a person borrows a motorcycle they also need to check with their insurer," said Janet Ruiz, of the Insurance Information Institute. "The person lending should also check on coverage. As with automobiles, policies vary and sometimes do offer coverage when you lend your motorcycle. It can be a costly mistake if you don't have the right coverage."
Many private insurance policies prohibit vehicle rentals, and pretending to have loaned a motorcycle that has actually been rented, in making an insurance claim, might be a case of fraud.
"And it's a felony," said Nancy Kincaid, of the California Department of Insurance.
Rothbard said his research indicated most transactions would be covered by existing policies and Twisted Road's coverage.
"All of the insurance companies we have spoken to state that their motorcycle policies cover liability when renting a motorcycle," he said. "As for damage, this was inconsistent, and depends on the policy issuance state and the carrier. In cases where there is damage, and the rider's insurance won't cover it, we will step in and cover the damages."
So far, Rothbard said, that's only come up a few times, and in no instance so far has the bike owner not been compensated for any damage to his motorcycle.
That convinced Desy, who said he wasn't worried about insurance issues because his policy covers anyone to whom he lends the bike.
"And Twisted Road said they would cover any damages, and they would cover theft," he said.