People who spit on the sidewalk (or actually who spit pretty much anywhere for that matter). For some reason I find that to be one of the most disgusting things people can do. Even tho I'm fairly sure I step in far more disgusting things during a day.
Either way, nothing makes me cringe as much as that. I still remember this one kid who'd occupy the bench at our bus stop and just sit there and occasionally spit half a river onto the ground below him. Sometimes the puddle had slimy lumps in it as well. Once he got up because an old lady approached. She sat down, but before she did, she walked right into that mess and the way it clung to the bottom of her shoe almost made me throw up. I still feel kinda sick when I think about it.
*First world problems deluxe*
It's phlegm. I do the same, because it sits in my throat and irritates it. There's no reason to blame themselves, but their health.
That's why you swallow the phlegm, not spit it out. Or at least do it in a location that is not the sidewalk. That's what I do the few times I get that.
Besides, if it's an action that annoys someone, it's an action that annoys someone. There are plenty of actions I find annoying, but I don't hate on the person doing them unless they are doing it purely to be an asshole. Sometimes annoying actions are necessary. That doesn't make them any less annoying.
Anyway, the playful SCREAMING of children. My neighbor has two girls who often scream like they're being murdered while they're playing outside and I don't friggen get it. There is NO reason to scream like that.