Proxemics (#103)
In the last two years we've learned a lot about what it means to be (or not to be) near each other. Proxemics is the study of how people structure the space around them and what zones they perceive meaningful. The anthropologist Edward Hall described four different reaction bubbles: farthest away the a public space, a social space, a personal space and an intimate space (which, according to Hall, corresponds to: lovemaking, comforting, protecting, playing football and wrestling. The guy knows his priorities.)
This distance awareness is not universal and differs between individuals and cultures. Usually, the closer another person gets toward your intimate space, the importance of nonverbal communication increases. That's one reason, why we tend to stare at our smartphones or into the distance while standing in a jam-packed subway. It's like trying to annihilate the physical contact by pretending the other person doesn't exist.
And if you don't care about boundaries, you could do it like Panamanian Capuchin monkeys. In order to greet each other, they just stick their fingers up each others noses.
https://www.sciencedirect.com/topics/medicine-and-dentistry/proxemics
https://www.nationalgeographic.com/animals/article/monkeys-perform-strange-rituals-to-test-friends