A high five is great way to communicate happiness, celebration or affection between friends, without the formality of a handshake, or the intimacy of a hug.
When to high five:
The perfect occasions for high fiving are sports matches, parties and other social gatherings, especially when there’s something to celebrate. Don’t use high fives in a job interview, boardroom meeting, or other formal event. And never high five someone who has their hands full.
Oh, and giving high fives on an escalator in a crowded subway station are apparently also acceptable!