I think the most annoying thing for me is not any single comment, but the assumption that by having curly hair, you aren't taking care of it.
People have this weird idea that it's easier to take care of curly hair instead of straight hair.
Once somebody said that they envied my hair because it was so easy to take care of and they wished that there hair wasn't so straight and difficult to maintain.
I'd had a rather bad day, so I launched into a recitation of everything I do to my hair: the first CO-wash, the second CO-wash, the way I lean over in the shower to give my hair volume, ACV rinses, the adjusting of water temps, the gels, plopping...
I just get tired of curly hair being seen as the "easy" way out or hair care.