@Eldistan
Writing "tsundere" well is a science unto itself. The issue isn't the harsh behavior on the outside, the key is that there has to be a golden core at the center. Taiga may be prone to violent outbursts, but as the story unfolds she is shown to be noble, caring and self-sacrificing. While YuujiI don't want to spoil Toradora for anyone so I won't go into detail.
Kaoru is completely aware that his love is unrequited, that Waitress sees him entirely as a platonic friend who is clearly trying her best to anticipate and manage his capricious outbursts (that's the part that's toxic! The physical violence is mostly just gross, it's how he uses it to exert control), but rather than support her (as a friend should!) he sabotages her romantic aspirations every chance he gets and punishes her for not complying with his own selfish desires. If he's supposed to be a tsundere type character intended to be loveable, he's an unmitigated failure.
There is no golden core.
I don't think that's what the author's going for, in all fairness. I think Kaoru's supposed to be exactly what he is - a villainous antagonist who has to be thwarted by the hero actively pursuing the love interest rather than just admire her from afar.