Well, "rude" is the clear winner, with 54 occurrences (and one "intentionally rude"). Runners-up:

    harsh                           21 ("overly harsh": 2; "too harsh: 1)
    negative                        13 ("unduly negative": 1; "completely negative": 1; "overly negative": 2; "negative Nancy": 2; "too negative": 2; "totally negative": 2; "intentionally negative": 1)
    snarky                          12
    overly critical                 11 ("too critical": 3; "critical": 3)

Other common phrases:

    an ass                          8
    pedantic                        8
    argumentative                   8
    insulting                       6
    a downer                        6 ("(a) Debbie Downer": 2; "down": 1)
    dismissive                      6
    flippant                        6 ("flip": 3)
    offensive                       7 ("blatantly offensive": 1)
    cynical                         5 ("overly cynical": 1)
    condescending                   5
    glib                            5
    a jerk                          5
    mean                            4
    pessimistic                     4 ("overly pessimistic": 1)
    that guy                        4
    crass                           3
    curt                            3
    a hater                         3
    disrespectful                   3
    patronizing                     3
    presumptuous                    3
    nit-picky / nitpicky            3

Terms that were only used twice: obnoxious, picky, insensitive ("culturally insensitive": 1), discouraging, crude, impolite, preachy, a tease, adversarial, coy.

HN has quite the vocabulary. There's a long tail of single occurrences: meta (ed: ha-ha), naive, cheeky, shortsighted, dumb, hasty, racist (ed: surprising!), stuffy, demeaning, snide, dense, nasty, personal, unhelpful, contrary, contentious, fanboyish, cold, doom-and-gloom, frivolous, facile, accusatory, callous, lame, inflammatory, hating, ironic, skeptical, trolling, trollish, patronizing, spiteful, sexist, disagreeable, controversial, simple, overly reductionist, hard on Aussies (ed: chuckle), antagonistic, off-topic, crabby, crude, derogative (ed: think they meant derogatory), passing absolute judgement, an idiot, an alarmist, an insensitive dick, a curmudgeon, an HN curmudgeon, a troll, a jackass, a tweak, a word Nazi (ed: surely not), a grumpy gus, a dick, a total dick, a stickler, a hardass, a killjoy, a huge downer, a turd, a burden, the grumpy skeptic ...

...and my personal favorite:

"the next snarky Lisp guy in the room".

There were about 7 other things roughly fitting the pattern here, but not quite within the spirit of the rest: e.g., "trashing Ballmer", or "overly favorable towards Google".

Quoted text was ignored where possible; instances of "or", as in, "insensitive or rude", counted as a point for each, except for "or anything", which was ignored. Terms were very lightly massaged, for example, "so callous" would have counted simply as "callous".