Calling names ("fanboy"), doubting what someone has or hasn't done, telling them what they don't understand, drawing personal conclusions from reading extraneous things they've written and importing that into an argument as ammunition.
None of those things is necessarily a personal attack by itself but they're personal, uncivil, and especially bad in combination.
We detached this subthread from https://news.ycombinator.com/item?id=11789509 and marked it off-topic.