Is it normal for a sister to do this
i got home the other day and i was soo horny i just had to wank as my gf is away for work. while i was wanking i thought of my gf and her sexiest lingerie so i went to grab it from the washing. so anyway i got them and started jerking off with them and rite as i burst my sister walked into the flat (she is staying with us for the Easter holidays she is 16 and in her final year of school) she saw me cum and just stood there for a few seconds then walked up to me took the pants i just burst over and said i guess I'm gonna need to wash my pants again . i did not no my sister had the exact same pair . Now she keeps wanting me to jerk off on her pants and bras and let her watch . is this a common thing for teenage girls or what I'm so confused and need advice on what to do.