The fatal shooting on Wednesday of a top UnitedHealthcare executive, Brian Thompson, on a Manhattan sidewalk has unleashed a torrent of morbid glee from patients and others who say they have had negative experiences with health insurance companies at some of the hardest times of their lives.

“Thoughts and deductibles to the family,” read one comment underneath a video of the shooting posted online by CNN. “Unfortunately my condolences are out-of-network.”

On TikTok, one user wrote, “I’m an ER nurse and the things I’ve seen dying patients get denied for by insurance makes me physically sick. I just can’t feel sympathy for him because of all of those patients and their families.”

The dark commentary after the death of Mr. Thompson, a 50-year-old insurance executive from Maple Grove, Minn., who was also a husband and a father of two children, highlighted the anger and frustration over the state of health care in America, where those with private insurance often find themselves in Kafka-esque tangles while seeking reimbursement for medical treatment and are often denied.

Messages that law enforcement officials say were found on bullet casings at the scene of the shooting in front of a Midtown hotel — “delay” and “deny” — are two words familiar to many Americans who have interacted with insurance companies for almost anything other than routine doctor visits.

Mr. Thompson was chief executive of his company’s insurance division, which reported $281 billion in revenue last year, providing coverage to millions of Americans through the health plans it sold to individuals, employers and people under government programs like Medicare. The division employs roughly 140,000 people.