The original triggering
It starred a young Rob Reiner as Mike "Meathead" Stivic, the young, progressive, liberal, hip-to-the-jive leftist who serves as a sharp contrast to Archie Bunker's supposedly antediluvian way of looking at the world. The show's producer, Norman Lear, originally intended for Meathead to be the sympathetic character that the audience would relate to- and he intended Archie Bunker to be the redneck loudmouthed idiot that the audience would instinctively loathe.
As we all know, now, he got it completely and totally wrong.
In reality, the American heartland quietly loved the Archie Bunker character because he reflected them. He spoke for the "Great Silent Majority" that believed in America's founding values of hard work, the dignity of the common man, limited government, peace through strength, and personal responsibility.
Meathead represented everything that the average American truly hates: whiny neediness, dependence upon others, and worst of all, a sort of effete limp-wristed weakness that can only be described to the modern eye as "quintessentially French".
(There was a time when calling the French "weak" was beyond idiotic- this was back before WWII, when France was still a Great Power and was, in fact, considerably stronger and more technologically advanced than just about any European power. If you look at the Frogs these days, though... Well, I imagine that Napoleon is spinning so fast in his grave that his corpse has created its own microgravity.)
Looking at these clips of the two antagonists in action, it's not difficult to see just why it is that Meathead was so easy to mock- he got triggered so easily: