agreed, it's foul - that and the pre-spit throat-clear. hchrhchrhchr. yech!!
but i think it's maybe a cultural thing, so needs to be properly addressed, probably with a reintroduction of the public health warnings and fines many of us can remember from the buses of our childhood.
incidentally it is somewhat harmful to swallow what is essentially a waste product which the body has worked hard to separate and eliminate ~ which is the primary reason it should NOT be spat into a public place. humans should "catch their germs in a handkerchief" or some other convenient receptacle, ready for proper hygienic disposal.