I've chatted with strangers on climbs and met lifelong friends at the dirt jumps.... I can't see much excuse to ignore fellow riders. Simple trail etiquette, like yelling out "there are three more", "on your left", or "have a good ride" is all that's needed to connect with people, and more importantly, to not be a dick.
The Bakery: Don't Be a Dick, Talk to the Bun Guy.
The Bakery: Don't Be a Dick, Talk to the Bun Guy.