Underwood said Gen Xers might be more likely to come to Las Vegas to explore the striking rock formations outside of town.
"You're probably going to take a hit with this generation," he said.
That pronouncement did not sit well with some grunge generation attendees.
Kristi Miller, who works for an online travel booking company, spent lunchtime railing against Underwood's apparent resignation.
"What's going to happen when the boomers start dying if we haven't gotten Gen X on board with our brands? I don't think the tourism industry should take that lightly," she said.
Millennials, many of whom are still too young to set foot on a casino floor, sounded a bit more promising. Underwood advised executives to set up programs that reward 20-somethings for just showing up.
"It's not their fault. It's what they grew up with — everybody got a trophy," he said.
Underwood also recommended tapping into the generation's patriotism and spirit of social involvement.
"They have been described as Generation Give, and there is an enormous opportunity for you in this," he said.
Millennial Jenny Patterson, who books hotel rooms and shows for tourists, said the workshop convinced her of the need to target specific demographics more consciously, instead of always going for a general audience in her marketing. She was especially grateful for the insights into the mind of the older gambler.
She'd intuited that baby boomers are more likely to pay for convenience and service, she said, "but I'd never really understood the 'why' of it."
Cory Brooks, who runs a charter place service out of Las Vegas, said he planned to take Underwood's advice and make more emotional appeals to his older customers.
After the talk, several members of the audience could be heard defending their generation to a group of older or younger people.
Hannah Dreier can be reached at http://twitter.com/hannahdreier