Bad grandma

I remember my moms parents were such good grandparents to my brothers and I. My mom is now a grandma to my three year old son and she just doesn’t seem like a good grandparent in my or my SO’s eyes. She gets really annoyed with my son easily, tells him to go away, when she “babysits” (her words, which I hate that term) him, she barely gets out of bed and just puts the tv on. She doesn’t do anything for his benefit. I have been told to cut her out of my life a little bit until she learns boundaries but idk how. We have a rocky relationship. I am constantly walking on egg shells with her because she gets mad easily. And she has yelled, and cussed me out in front of my son on several occasions. When I tell her to TALK like an adult instead of yelling and cussing in front of him, she tells me to fuck off.

IN FRONT OF HIM.

She yells at him in public at stores and we get stares. I feel like I should stand up to her but it would cause a huge fight. And she does/can/will get violent.

My boyfriends family is so amazing and then.. there is my parents....

What should I do