Is it bad luck to wear a hat indoors?

If you are into superstition, yes. Otherwise it’s only a social faux pas.

It’s quite rude to wear a hat when you’re indoors, especially when you’re eating.

That’s a pretty big generalization. Its very dependent on the situation.

I think it depends on how you define bad luck. If whomever you’re with considers it rude, as many do, you may not be accompanying that person again any time soon. If it was a sort of “date” situation, it could then be considered bad luck.

There is a superstition that it is bad luck to put a hat on a bed. This is also mentioned in the movie “Drugstore Cowboy”.