It's difficult to make a comment about a past action or situation in English, as often you need to use complex grammar. By the time you remember the structure and the rule, and then think about your reply, the conversation has moved on.
But there is an easier way. Here are some "fixed phrases" that you can use to criticise a past action or decision. Don't think too much about the grammar - just use the complete phrases, and add the details (your comment) to the end of the phrase.
Here are some examples:
You should have ... (+ past participle)
When you want to say what the ideal action was, you can use "you should have" and follow it with the past participle of the verb. Here are a few examples for you:
You should have told me. (= But you didn't tell me, and so I couldn't help you.)
You should have called. (= But you didn't phone me.)
You should have left the motorway at the other junction. (= But you didn't, and now we are lost / late.)
Check the pronunciation here. Notice how the "have" sounds like "uv".)
You shouldn't have ... (+ past participle)
When you want to say that a person did something wrong, you can use "you shouldn't have" and follow it with the past participle of the verb. For example:
You shouldn't have done that. (= But you did, and now you are in trouble!")
You shouldn't have spoken to her like that. (= But you did, and now she's upset with you.)
You shouldn't have eaten so much last night! (= But you did, and now you feel sick / uncomfortable, etc.)
Check the pronunciation here. Remember that the n't of shouldn't is very difficult to hear.
Why didn't you ... (+ infinitive)
Here's another phrase we can use to criticise. We can use it when the person didn't do the ideal action.
Why didn't you call me last night? (= I was waiting for your call!)
Why didn't you ask for help? (= I was able to help you.)
Why didn't you look at the map before we left the house? (= You had the time then, and because you didn't look at it, we're now lost.)
Check the pronunciation here. Remember that your voice will probably fall at the end of this sentence.
Be More Fluent In English
A quick way to speak English more naturally is to use "fixed" expressions like the ones above. They're easy to use because they never change - all you have to do is add the detail or your comment.
In my fluency program Real English Conversations, I show you the most common expressions like these - so you can speak English more fluently.