Fetish for sniffing and licking armpits

My stepbrother is so weird, he confessed to me that he had this fetish for his armpits, I didn't know what to say but he looked so embarrassed that I wanted to cheer him up, I said, do you want to see mine? everything got out of control when he started to sniff and lick my armpits causing small giggles and moans to escape.