My friends brother came to me several times for kissing lessons!!?

okey so my friend'e brother keeps comin to me for kissing lessons and i keep telling him NO, but he wont seem to listen. he says he never kissed a girl and he really wants to learn but why is he coming to me!?!? like i really dont kow how to tell his parents, i told his sis, but she says he is only messin around..but i know he isnt..he comes when im by myself..like what should i do?