Don't apologize if you don't agree with your friend's excuse
Don't succumb and apologize unnecessarily if your friend offers a ridiculous excuse for ignoring you. Be warm and empathetic if there has been a misunderstanding but don't say sorry if your friend tries to blame you even when you are not wrong.
'I am sorry you feel this way but this was a complete misunderstanding' - Use a similar sentence if you and your friend hit a deadlock where both of you find each other at fault.