Boyfreind wants me to go nude in front of his brother?

ok i been dating my boyfreind about 5 months and we get along great he does everything for me and lol plus his family has a lot of money, he does a lot for me and been with me through a lot and he is 15 i am 15 and his brother is 13. he is obsessed with me wanting to be nude in front of his brother to see his reaction. he said his brother hasnt seen a nude girl in real life, and wants to see his reaction. he said he dont care if i make it look like an accident or if i just walk through nude in front of him but he just wants to see his reaction. why would he want me to do this, i just dont see why he so obsessed with this? should i give in to this he keeps on and on what should i do i dont feel 100% comfortable i could do it but it'd be a little un-comfortable kinda insecure? i just dont see why he so obsessed with this.