I'm planning on giving someone an ultimatum.
Why are you going to give them an ultimatum?
I feel like this person is backing me into a corner, into an intolerably painful situation.
I think that just removing yourself from the situation will be the most effective here. Giving ultimatums to people is just going to cause more tension and drama!
I get what you're saying, but I want to do it. I want them to feel terrible.
I understand, but if you're already in a painful situation then laying down an ultimatum is only going to escalate the drama. The mature thing to do would be to take a step back from the situation and let things cool down.