Dear Miss Manners: My husband and I attended a wedding with a 1920s theme, where the guests were encouraged to dress in period costume if they felt so moved.
Many of the gentlemen who arrived in the suggested costume wore hats, to better convey the theme, and we all by unspoken accord wore them the entire evening (perhaps, subconsciously, in imitation of the groom, who did the same).
Later, it developed that the bride’s grandmothers and aunts had been much dismayed by all the gentlemen wearing hats indoors. Obviously, there’s nothing to be done about that now, but for the future what’s correct?
Gentle Reader: Gentlemen who lived during the ’20s were normally great wearers of hats, so they were sure about what to do. If you really want to be in character, you would therefore remove the hat indoors.
Arrrrrrrrrrgh.....of course Miss Manners and the grandmas are technically correct that hats shouldn't be worn indoors, and of course gentlemen of the day would have known this and never worn their hats indoors. But their hats weren't part of a carefully contrived costume, and these were. And if the whole wedding was indoors, they never would have gotten to wear their hats at all.
I think following the groom's example was the right thing to do in this case (the real point of etiquette, after all, is to prevent embarrassment and confusion among as many people as possible). Had he removed his hat, others should have as well--and they most likely would have.
Assuming the guys had the good sense not to wear their hats in the church, I think allowing your memory of your granddaughter's wedding to be overshadowed by your memory of uncouth young men in fedoras is a shame. Let it go.