My SIL was a bit entitled bridezilla when I was a bridesmaid.
I smiled in the face of it all, wore a (hideous) dress as requested, paid for said hideous dress. I was asked to tell my mother who had spent months upon months dieting and having her hair recoloured and was finally starting to get some self confidence that the dress she liked would "ruin the photos". It was classy navy blue. I actually refused that when asked because it was not only rude (my family paid for the wedding) but also ridiculous as my mother looked stunning. I mentioned to my mother that she could buy another dress in case she changed her mind, my non-swearing mother immediately said "those b*, what did they say?" Good one mother, exactly that:)
I meanwhile was told to gain weight, because I was slimmer than the other bridesmaids. Seriously, told me to gain weight. My purse was lighter after paying for them! I was also asked to not have a tan because everyone was different nationalities and they wanted a mixture of ethnicities. I always have a tan. It's called, my skin.
All this I nodded and smiled, other that telling my DB that he was being a selfish twat destroying our mother's self confidence.
One thing I refused though, other bridesmaids saying we should wear our hair up. Don't know you random strangers, it's my brothers wedding, who are you and I'm not exposing that much skin! So my long hair was down to cover my shoulders, back and any shape of too much cleavage. I didn't say anything, just said to bridezilla, I think I'll have down style, is that ok? If she had said no, I would have said I'm sorry, I can't wear such an exposing dress in public, to a formal affair (which we are paying for) with all my family and photographers there.
IF she told me to not wear a bra, I would laughed and said "Nope, this gig is not for me".
Dictating your undies, keeping the dresses hostage and expecting you and others to not wear a bra and worry about boobs everywhere?!
Seriously, at that I would say "I'm sorry, I can't wear that without underwear and I wish you hadn't asked as it's not fair to force me to be so uncomfortable, I don't think I should be a bridesmaid".
Then get a tan, wear your hair down, don't pay for anything, tell every mother she looks fabulous and if you are invited, go to Morocco for the weekend with the other girls who need underwear!