You are a 15 year old boy and your friends mother tried to put her hand down your trousers what do you do?

In what manner did the friend's mother put her hand down a boy's trousers? Was she just trying to tuck his shirt into his trousers? Was it with malice? Was she touching him inappropriately? If there is a suspicion of sexual harassment then seek advice from a trusted adult or parent about it.

Tell her that you will tell your parents if it or any other sexual intimidation happens again. The easiest thing to do is stay away from your friends home though.