Whats the most pompous thing Mankind has ever done?
Humanity, in my opinion, has never really been united or cohesive enough for any one act of pomposity to be laid at the feet of all of us as a whole. Various cultures have done extraordinarily pompous things, but as a whole, I just don’t see it. But on a less-than-global level, I think the luxury liners of the early 20th century would qualify. Look what happened to Titanic, for instance – there’s just no justification for all that splendor and majesty if one is looking at it with a philanthropic eye. WWII and nuclear warfare would certainly qualify for another one, imo.