How could you do that!

@Language learner posted:

A: I will ruin his life.

B: How could you do that! He has done so much for you, after all.

Can I use "could" in this sentence, where the action of ruining his life hasn't yet taken place? Is "can" possible?

I know the following are possible:

How could you say that!
How can you say that!

Hi, Language learner—In the context you have given, what would be the most natural is this: "How can you think of doing that!"

@David, Moderator posted:

Hi, Language learner—In the context you have given, what would be the most natural is this: "How can you think of doing that!"

OK. But are these also possible?

"How could you think of doing that!"

"How could you have thought of doing that!"

@Language learner posted:

OK. But are these also possible?

"How could you think of doing that!"

"How could you have thought of doing that!"

They are possible in other contexts. I would not use it in the context you have provided. I would instead use the sentence that I would told you I would use.