I was under the impression that it was an etiquette no-no. I only dry fired a gun once and it was at the insistence of one of the shop clerks so I could get a feel for the trigger.
Other than that I make a conscious effort to not dry fire any firearm that isn't mine whether it's a friend's gun or I'm at a shop.
Other than that I make a conscious effort to not dry fire any firearm that isn't mine whether it's a friend's gun or I'm at a shop.