I don't do adult themed cakes either. The customer is NOT always right. No matter what anyone tells you. They are Not entitled to anything you feel uncomfortable making. I have worked in retail for decades and can finally just say that out loud and I mean it!
I don't have qualms about breaking up with a customer if after great service, nothing I can do will make her/him happy. There are plenty more where she came from, and who needs the stress? I KNOW I bend over backward for my cake buyers. It's not about money.
I had a girl a while back who placed an order. It was her second order, so I thought we were friendly. She loved her first cake. I left a message a few days before her cake was due to ask if there were any changes, but needed (what ever) details from her before I could bake it. So I needed to know as soon as she could let me. She never got back, so I left another message the next day "Hey I need this info ASAP so I can get ingredients and the cake baked, etc ..cheerful like always, smiley face. (ASAP=as soon as possible, which means just that)
She finally FB'd me and said "OK. I'll let you know what I decide, ASAP." Intuition said "uh-oh" So I waited to see if she'd be forthcoming with the info.. FB'd one more time before firing up the oven "Hey, baking today, need to know your info, hope to hear back "
Her next message? " I'll let you know, ASAP."
UN friended her and I don't care where she gets her next cake. I do not want her money because of the disrespect that would come with it.
YOU are the person making the super fancy, covered in everything, custom to their specs, excellent tasting masterpiece for their once in a lifetime event! They need you!
Be friendly, but firm!.