I'm not sure what wording you used but thought I'd detail my experience which might chime with yours.
I used to bottle up my rage and then eventually explode like Mt Vesuvius.
Then having Vesuviused a boss, (who frankly deserved it

), I was sent for assertiveness training.
There I was categorised as an aggressive and not non assertive as I thought I'd be.
The gist of the course was to get the person who had pissed you off to explain themselves. Most people back away from this in normal life and let them get away with their behaviour whilst quietly fuming.
So you have to give them open ended questions or a statement in reply to their questionable behaviour or words.
For example - "that's not a very nice thing to say", (statement), or "why would you say that?" (open ended question).
Basically using the how, what, why, when in your question in reply
AND THEN
To say absolutely nothing but look at them
Don't try to save them as you start to feel sorry for them because of the awkward silence
Because you haven't given them a reply where they can just say yes or no they have to explain themselves re their behaviour and/or words.
Keep calm throughout and keep on with the how, what, why, when questions after their reply if you need to.
I immediately tried it on 2 people - one a bossy person who'd descended on me with their family and children when I'd been in my house a day. The woman was pretty scary as they lost their temper, but I stayed calm and kept on with the questions and they stormed out.
Their partner followed with the kids looking apologetic.
The second time was with a con merchant boyfriend of someone I knew. I wanted to know the truth about something he was doing, which he ended up blurting out against his will with my relentless questions and silences.(He looked very shocked that he'd dropped himself in it).
I felt very empowered and if you do it with witnesses it's even better, as they can't say you're a bitch as you were only asking a question whilst being calm. They get angry or freaked out that they can't control you.