We were discussing flame wars on Slashdot before News.YC (ahem, Hacker News) even existed. People on the internet before then were discussing flame wars on usenet (as the parent post mentions).
We had perfectly good flamewars on BBSes in the 80s, and it only got worse once fidonet sprung up.
And before that on ham radio bands like 80M and to a lesser extent 20M we had plenty of people arguing over basically nothing since... I donno 1920s or so?
We were discussing flame wars on Slashdot before News.YC (ahem, Hacker News) even existed. People on the internet before then were discussing flame wars on usenet (as the parent post mentions).