The line that gets me is "the homeowner has no idea." Good. They shouldn't. Most people have no clue what depth their cabinets are and they never will. The 12 inch "standard" came from a time when kitchens were smaller and plates were thinner. Plenty of custom shops run 13 or 14 on purpose, and designers ask for it all the time to fit a deeper microwave or a bigger plate stack. Your old boss laughing about it tells you everything. It was a choice, not a mistake, and it worked for ten years of customers. Nobody has ever walked into a kitchen and said the uppers stick out too far unless they were already looking for something to complain about.

I read somewhere that fighting over food is like the number one reason roommates stop being friends, so a lock sounds less like a band aid and more like the smartest $180 you ever spent. Sounds like it lasted fine because it killed the problem at the source instead of making you both fake nice about it.