Sometimes as I people-watch, I pretend I’m an alien, and try to imagine how strange the things we do might seem to someone with no experience with humans. In no particular order, here are a few I enjoy feigning ignorance about:

The morning coffee ritual– Sleep inadequate to recharge daily energy levels in adults. Supplement required for productivity.
Children playing pretend– Instantaneous construction of increasingly complex false reality, usually while (mostly) conscious of its falsehood.
Singing– Experimental noises from the human throat meant for entertaining others or oneself. Usually louder and noticeably more tonal than speech.
A crowd at a sporting event– Adults playing pretend; two armies clash with one clear victor. A simple sense of morals, similar to their young.
Young women doing each other’s makeup– Bonding through mutual assistance to increase mating appeal.
Funerals– Collective support through gathering and discussion of deceased with acceptable (often encouraged) demonstrations of a sense of loss (in some cultures).
Dancing– Demonstration of physical ability through study and imitation of traditional movements. Self entertainment, a form of relaxation through solitary or collective physical movement, usually accompanied by music with strong attention to percussive instruments. Demonstration of rhythm (the ability to anticipate the next iteration of a percussive sound) and physical coordination to potential mates. Movement for the sake of movement.
Meditating– Attempt at alternate thought patterns and occasionally the eventual abandonment of the body through total lack of movement, vision, speech and interaction with anything.
Kissing– Physical contact, specifically with the lips, of one or more people to demonstrate romantic, sexual, or familial preference or greeting.
Telling a joke– Attempt to elicit a joyful reaction from others, usually to bond or gain acceptance.