We all have this problem from time to time, someone says something and inside our head we already have out answer ready, and sometimes it can be harsh because what the other person said is
harsh too. All of this is coming from the ego.
We forget that by being silent we are actually stronger than the other person, on that moment we don't put ourselves in a bad arguing or even a fight, and stay neutral protecting ourselves because
it is not worth it to put so much energy in those who only mean harm.
For the other person it is easy to do but for someone who likes to get his word out I understand that it can be difficult, to walk away and say nothing.
I do agree that there is nothing wrong by standing up for yourself and defend yourself  but it can be easy to do this in a neutral way and like I said by not giving your energy to others.

Shielding yourself can help. Also try to make contact with your higher self it will always speak in a lovely way and is not harming others and yourself.
How do you know when you are in contact with the higher self, it is not so difficult first of all you need to calm a little bit otherwise emotions will get the hand in it, once you are a little bit relaxed
you can before you speak open your crown chakra and throat chakra or ask Archangel Metatron to do this for you if it is not working because you are too busy. Trust that he is doing this for you.
When words come to you wich are not harmful you know you are in contact with your higher self.

To get more in contact with your higher self you can meditate, by releasing energies from others by giving it back to them ( the energy will get out of your aura ) and your own will come back in the light sparkle just above your crown chakra. once you did this you can flow the energy into your chakra. Finish it by grounding yourself otherwise you will fly a little bit.