Maybe type or write out things you want to say, just to vent it out without actually hurting anyone's feelings? I used to think that was trivial and pointless, but I've really found it so helpful, especially when I'm at those near breaking points. I pretend I'm going to give them the letter, but I know deep down I won't, that way I write it as if it's to them but since I'm not giving it to them I can be brutally honest.
I also think certain people are really understanding when someone says something to the effect of "I'm really dealing with a lot right now, I'm going to do my best not to get upset with you but wanted to say up front that I'm pretty frazzled" ...sort of humanizes you and connects you with that person in what could be an otherwise polarizing/isolating experience
But, if you're not dealing with safe people then that could backfire....that's when I just vent to other people instead.
At any rate, you're safe here and you're heard!