He was buckled into a window seat from Tampa to Philadelphia on Sept. 23, when a large man sat down in the middle seat next to him.
Lapin could not lower the armrest between them, he said in an interview, and he spent the next two hours and 15 minutes "scrunched all the way over by the window."
In the United States, there are no government regulations for accommodating overweight air travelers. It's left up to the airlines, which until recent years "didn't have clearly stated policies to deal with passengers of size. Now, they do," said George Hobica, founder of Airfarewatchdog.com.
More airlines are enforcing "customer of size" rules, which range from requiring such passengers to purchase additional seats to, in some cases, refusing to board them.
"Keep in mind that these rules are observed on a case-by-case basis," Hobica said. Enforcement is up to individual airline employees, "and many may feel uncomfortable acting as the 'fat police.' "
Coach seating - six seats across, in three-by-three arrangements - is skimpy for the average-sized, much less the large and tall, he said.
"Arnold Schwarzenegger, in his heyday, probably didn't fit in a standard 17-inch coach seat," Hobica said.
Meanwhile, airlines are packing more people onto planes, as jet fuel and other costs have risen, but seats in coach are not getting bigger.
Although airline policies suggest that the person buying the ticket should know whether he or she can fit in the seat, some travelers have encountered humiliation at the gate or when boarding.
Kenlie Tiggeman gained national attention in April 2011 after a Southwest Airlines gate agent told her she was "too fat to fly without an additional ticket."
"He asked me what my weight was, what size clothes I wore. I was on the fourth leg of a Southwest flight," said Tiggeman, a New Orleans resident who blogs about weight loss on her website, AllTheWeigh.com.
She weighed 284 pounds at the time. "I could put the armrest down and wear the seat belt."
After informing the agent she had a weight-loss blog and was going to record him with her iPhone, he allowed her to get on the flight. Southwest contacted her the next day, apologized, and offered her a free flight voucher.
Tiggeman flew several more times on Southwest without incident, and then last November when she checked in for a flight, she again was told she had to buy a second ticket.
"My problem with Southwest is that they need to be consistent. On one flight, I don't have any trouble. On another flight, I have an issue," she said in an interview.
"They need to take the power out of the hands of the gate agents. Make it the same policy every day. If they want our height and weight, fine," Tiggeman said. "I'd much rather give it via the Internet when I buy my ticket than at the gate."
On the flip side are travelers who have had their personal space invaded by seatmates spilling over their seats onto the armrests.
US Airways passenger Arthur Berkowitz said he had to stand for most of a seven-hour flight from Anchorage to Philadelphia in July 2011 because a man weighing at least 400 pounds was in the middle seat next to him.
Berkowitz asked flight attendants about moving but was told there were no other seats. The airline later apologized and offered him a $200 voucher.
At the time, Berkowitz said, his primary concern was safety - he could not use his seat belt during takeoff and landing because the man next to him was sitting on top of it.
Berkowitz said in a recent e-mail that he had corresponded with the Federal Aviation Administration, the Department of Transportation, and the airline. "I tried a year ago. With the FAA and DOT and US Air. I'm done."
Policies vary and change, according to Airfarewatchdog.com.
Delta Air Lines does not require larger customers to buy extra seats, but may ask them to move or wait for another flight with more seating. Delta suggests that travelers purchase second seats if they think they are needed and can't wait for flights with empty seats.
United Airlines requires that passengers fit in the seat with both armrests down; if not, they have to buy second seats. "Those who decline to do so or upgrade to larger seats risk being refused at the gate."
US Airways says it "takes it case by case, offering extra space when available - and may require waiting for a later flight." Passengers who refuse to change flights may be required to purchase second seats at the gate, although the policy is rarely enforced.
Southwest requires customers to buy second seats if they cannot fit between the armrests. Southwest will refund the cost of the extra seats - after the trip and if the flight was not oversold.
Recently, Southwest revised its policy to say that passengers can get second seats free of charge at the gate. The airline recommends that passengers buy second seats in advance if they need extra room, but they can request refunds after the flight.
US Airways spokesman Todd Lehmacher said: "Our first goal is to try to accommodate the customer on their originally scheduled flight, by moving seats, if necessary. If that doesn't work, we will offer a later flight.
"It's rare," he said, "but if we need to compensate a volunteer to take another flight, in order to accommodate the person of size, then we will."
Contact staff writer Linda Loyd at 215-854-2831 or firstname.lastname@example.org.