In one of my recent Spelunky runs, I had an item that allowed me to see gems embedded in the ground/walls. Two particularly lucrative gems were embedded in a shop's ceiling, and I assumed the shopkeeper would not begrudge me giving him a new skylight. Boy was I wrong.
Seeing how I do not consider being murdered by shopkeepers a good way to end a run, I would like to know which actions they consider hostile.
Removing items from their shop without their consent
Carrying out mining operations in the near vicinity of their shop
Refurbishing their shops without a work permit
Handling live explosives while inside their shops
Assaulting the shop-keepers or their staff
Targetting the shop-keepers or their staff with flying or falling objects
Abducting the shop-keepers' staff
Bowling a huge boulder through their shops
Unsolicited visits when at home (vault)
Unwrapping presents early
The shop-keepers come from a single family and word gets around fast underground. Any report of misdeeds by the spelunker or any of his associates, the inhabitants of the mine, will be met with swift and fair shotgun justice.