I have always drawn the line for myself by differentiating between the action and the player.
I can be pretty direct and aggressive but to the best of my abilities I say things like "that's terrible play" "those reads are horrible" "you're gamethrowing" instead of "you suck" or "you're bad" or "you're a cheater".
Simply speaking say "that's a lie" don't say "you're a liar".
A player can be a good player and do something badly/misplay/have bad reads/etc. Calling their action bad does not reduce their skill level.
Ftr I don't know how I'm perceived maybe I am still offending people by this. I hope not The point is just sometimes you need to push your scumcases and have to be direct and confident. If people think you are vague, hesitant, or unsure they are probably not going to vote alongside you and might even scumread you for it.