Gliding down the bike path on a Saturday morning, you whip by somebody peddling in the opposite direction and give each other a nod. For a moment it's like "Hey, we're both doing the same thing. Let's be friends for a second.
The [Five Second Rule] has many variations, including The Three Second Rule, The Seven Second Rule, and the extremely handy and versatile The However Long It Takes Me to Pick Up This Food Rule.