Whitney Miller agreed: "It was, 'No, do you have a problem? Do you need to be removed from this aircraft?' And we responded, 'No, like, we don't understand what's going on. What's happening? Please tell us what's happening'."
A passenger behind the Millers began recording a video apparently after the pair were asked to leave the plane. In the video, a male flight attendant tells the Millers that they had "threatened us", while another flight crew member suggests that the airline could call the police.
"You're going to call the police?" Miller asks.
"What did we do wrong?" Whitney Miller can be heard asking. "Why are we getting kicked off this airplane?"
Finally, Miller raised his voice as he got up from his seat.
"This is the most loathsome experience I can actually say I've indulged in 70 years of flying on an airplane. This is absolutely incredible," he declared in the video. "We have a conversation. You're threatened. And we're going to have to leave after spending 12 hours in this airport waiting for this plane to leave. This is loathsome."
Miller could be heard shouting as he exited the plane: "Absolutely loathsome. Beyond the pale. This is a shameful experience. Absolutely shameful."
Frontier representatives did not respond to questions sent by email on Sunday morning. Airline spokesman Richard Oliver told Fox News that the Millers had made "disrespectful remarks" while boarding, including calling the flight attendants "stupid b***s," and that a flight attendant had alerted the captain.
"Our flight attendants are customer service and safety professionals who are trained to recognise situations that may impact comfort and safety of passengers and crew onboard our aircraft," Frontier said to Fox News. "The behaviours and comments exhibited by these passengers prior to departure were inappropriate; and as a result they were asked to leave our aircraft. Safety and security of our passengers and crew is our number one priority."
The woman who recorded the cellphone video said in a Facebook post that passengers can be heard clapping in the footage because they were supporting the Millers.
"Frontier is on my dislike list. These poor people did not deserve this at all!" Jocelyn Praia Gonzalez wrote on Facebook. "A stewardess felt threatened after 'overhearing' a conversation between this daughter and father just trying to get back after we all sat for a 9 hour delay! You hear his reaction? Still classy after all the attacks Frontier gave them both. Never again!"
Gonzalez did not respond to a request for comment on Sunday.