To lower your gun in Destiny all you need to do is stand/crouch/sit for exactly 5 minutes and it will lower by itself. Your gun will pop back up if you use the triggers, use the bumpers, use a super, look at an enemy, or get off a sparrow. Emotes will work and nav mode will too.
Have fun being a pacifist! ;p
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Bump from orbit, just to make sure.