The phrase first of all has long been used in everyday speech to signal that a speaker is about to correct, clarify or push back on something, and that familiar rhythm helped this short clip spread online as a reaction sound. It circulated on soundboards and in short video edits where creators needed an instant setup for a disagreement or a list of points. Its popularity comes from how recognisable the opening is on its own, so editors can drop it in without any extra context needed.