*TMI* mother/son relationship

my boyfriend is 25. his mother likes to squeeze his male parts and put her hand in his buttcrack *(not swipe like a credit card its more like she's trying to dig in there)* she would do it while he's sleeping or when his back is turned she would sneak and tell me shhh and then do it while saying "NUTS N BUTTS". it kinda puts me in a weird position because my bf hates it with a passion and gets really angry but i dont really know how to react because i dont want to get in their business and cause any problems. he is always telling her to stop but she just laugh and change the topic. i know it aggravates tf outta him because i see him trying really hard not to be disrespectful. to me it looks really distasteful and it makes me uncomfortable because of some situations in my past. i try to tell him its not normal and i suggested he go to her and talk about it so she could stop being annoying. tell me what yall think