What a great example and then also taken from life. I would have loved to meet your uncle :) thanks for this little insight into his habits.
To debate online, you probably always have to consider something like this as a positive sporting challenge to stay mentally stable. Those who engage in online arguments but feel neither the puff nor the humorous determination to conduct a debate according to unspoken rules (which we all know) can become victims of their own grimness and mistakenly blame the other person.
It is not impossible to counter very aggressive commentators in a way that changes the subject and shows a personal interest in them. Often aggressiveness is an expression of helplessness, but sometimes it is also a deliberate means used by, for example, matured personalities to test their opponent (just two out of many possibilities). Since you never really know, the tension is also the fun of having one. If not, it would probably be better to stay out of debating.
Have you ever succeeded in leading someone you perceive as an aggressor into a genuine conversation? That would be a good and interesting experience, wouldn't it?