Sometimes it's a cultural thing. From the Rose City Neighborhood in Portland to Sydney, Australia I've watched old Asian men spit like sprinklers. Humans are animals, and animals do gross shit. Last week I watched a woman change a shitty diaper on the 15 on my way home from work.
Everybody salivates but only straight men spit on the ground. This is obviously clearly not necessary, and probably dates back to the days when baseball players chewed tobacco.
I certainly enjoyed walking behind a nice gent the other day as he, so politely, hawked into the wind so his lung butter could mist my face. Delightful!