About your dad - you'd be surprised what people will put up with for the sake of having harmony for their children.

Don't let your mom make you her "buddy" in this matter. Be very blunt about how disgusting you find this behavior, tell her your brother knows (and is equally disgusted), and tell her it is going to ruin how you feel about her. Tell her if you ever hear another thing about it it, no matter how small, you WILL tell your dad.

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