Maybe she's not saying that you don't have a right to speak up, but perhaps, it's a method she's learned for dealing with him, that she finds effective?

Think of it, like steam from a boiling pot of water. If you keep it uncovered, the steam rises, and evaporates into the air. If you put a lid on it, all the steam stays inside where it condenses into droplets of water on the lid. Symbolically, the droplets are tears. When you are confrontational with a person who harbors deep anger, with no clear direction, everyone is unhappy and frustrated. If you let him blow off the steam, it goes in no particular direction, at all.

I found, the not quite 'ignore', but a rise about the anger, most effective, last night, with my stepbrother, that I haven't spoken more than two words to, in 23 years. I've seen him a handful of times, in all those years.

Man, oh man, doesn't your brother sound a lot like him. Living at home, contributing next to nothing, and as angry as he's ever been.

It was almost an adrenaline rush, to pull the non-reaction/'I'm more grown up that you'll ever be' manner of carrying myself when he had a little temper tantrum, when my son being an 8 year old boy, accidentally moved the tableclothe. Stepbrother, got a snide remark made to his mother, more a haughty remark/teasing remark to his mother, when she accidentally moved the table clothe, and when his anger diverted in my direction, shoulders up, facial expressions, priceless enough that he took his plate of food and returned to his room.

Rise above it, is how I am taking your mother's remark to you.