The mara, a South American rodent, even goes so far as to urinate in threat - but on subordinates. So do many rabbit species. Urination on another human is the extreme form of indignation. Spitting on someone seems to be a ritualized form of pissing on them - a ritualization accomplished by males and females alike. Cultures have contorted and modified the general repugnance humans have for urine and feces.
Some cultures tend to build up rigid taboos and others tend to treat it rather lightly.
I'm not sure there are any general rules. In our own culture people from rural areas seem to make less of it than urbanites. Maybe we tend to build up stricter taboos as our relationships become more intimate and our populations more dense. Rural blacks and sharecropper whites moving to the city have trouble at times in adapting to the organic aspects of urban ways. But the rural-urban principle doesn't hold up entirely.