While I can definitely see a lot of people trying to show off how smart they are on HN, they are doing it through demonstrating things and making solid arguments. On Reddit, that is usually done through personal attacks and demonstrating themselves.

So many times I went on reddit and saw someone making a solid argument, only to be derailed by someone going through their comment history and bringing it up as a "aha, gotcha" point in an argument. Even in cases where it shouldn't matter, something like seeing a poster getting downvoted to hell just because one of their comments wasn't critical enough of Trump in an argument that had nothing to do with politics and was purely technical.