Person: I'm really sorry.
You: No, you're not.
In my opinion, it's unbearably rude, and it's quite hurtful to the person making the apology. It also forces the conversation to stay on the topic of what the apologizer has done wrong, which is kind of unnecessary, because they already know they've done wrong. Hence the apology.
Also irritating: "'I'm sorry' isn't good enough."
If it's in the past, then there's nothing that can be done about it. So move on.