You should seriously reconsider whether sevenless was merely wrong or if he was attacking a massive group of people with completely baseless but very offensive claims, that were intended to provoke a response.

How would you respond if he claimed that Muscular Distrophy wasn't real, that doctors have made up their condition to make money, and sufferers just need to get over their awkwardness and work out more? Or if black people don't actually experience racism, that it's all in their heads, that human rights activists are just money grabbers, and they just need to work harder? Is that just being wrong? Or is that an attack on an entire group of people, intended to provoke?

I should have kept my calm. I'm sorry for acting out. But ADHD is a thoroughly researched serious executive function disorder that causes drastically higher incidences of violent crime, homelessness, joblessness, divorce, and severely diminished earnings potential compared to the average person. When you tell someone that has been a homeless and jobless college dropout, who with treatment has graduated college and gone on to support a family and hold down demanding jobs in the tech industry, that they are just imagining things, they tend to attack back.

I hear you. One way of de-escalating arguments is for people to speak from/about their concrete experiences, like you implicitly did in the last paragraph here. People who disagree strongly seem to find it easier to engage one another through that channel than by arguing in the abstract. Often, one finds that the other person's position is grounded in experiences of their own, even though they may have drawn incorrect conclusions from those experiences. That makes conversation easier.

Conversely, arguments in the abstract that are fueled by emotion coming from personal experience tend to get stuck, and nobody much enjoys them.