She was an 11 yog once, and should remember what it is like to be embarassed and proud at the same time. Sounds like she only has boys, and you only have girls.
Life is totally different for the whole family depending on gender.
My bf in hs, had a son and I had a dau, within 6mos. She and I have discussed this many times, and we agree that there is a possibility for problems. We don't agree on discipline, and occasionally have a tiff, but we eventually just agree to disagree, and respect the others wishes in their home. Maybe when talking to his mom, you should try to find common ground. Something both of you agree is wrong or inappropriate, then discuss ways to discourage it.