To offer perspective from a person who is like this, I have ADHD and through that RSD (rejection sensitive dysphoria) and before I got diagnosed, it was just as hurtful to me to be acting this way as it was to the person affected by it (NOT to diminish the effect of my behaviour for others, as it is my problem it is also my responsibility. At the time I just didn't know what the problem was and how to tackle it).
I didn't know why small things made me immediately jump to the worst case scenarios and conclusions, making me spiral into an endless loop of negativity. I hated myself for always "ruining the mood and fun", I isolated myself from social gatherings and relationships in fear of overreacting to small comments and ruining everything. I managed to convince myself for more than half a year that my own little sister, my best friend, hated me because of one offhand comment she made to me while tired. When she found out it broke her heart.
It's like rationally I KNOW that my sister could not possibly suddenly hate me after one comment but what the dysphoria does is that it throws all rationality out of the window. It is so frustrating and depressing to constantly deal with. When I found out, my life and relationships improved dramatically; I now know why I take comments like that so heavily, I've discussed with my partner about this and how it affects us, I've researched and tried ways to stop the negative looping in my head and now we're at a place where if my dysphoria kicks in, we know how to effectively communicate about it and shut the loop off. I always put a heavy emphasis on the fact that I do not want people around me to walk on eggshells to not trigger my dysphoria as it is my problem to deal with, but if they want to help me there are ways to say things in a different way that don't trigger anything (mostly it's about being as detailed and direct as possible, uncertainty and vagueness leaves too much space for the dysphoria to fill). There are also very simple ways to stop the looping if the dysphoria does get triggered, as long as I am able to tell the other person what caused it. In this case, all that would be required is for me to communicate “Hey, the way you said that made me feel like you insulted my music taste and as music is one thing we connect a lot about, it’s kinda spiraling me into thinking you don’t like me anymore. You said nothing wrong, my RSD is just kicking in.” All my partner has to say is something to the effect of “That is not what I meant at all, I love you and think you have a great taste in music, but we can’t obviously agree about every single song. Could you show me more songs that we both might like?” Communication. No blaming.
I’m just saddened to see the amount of people in this thread and elsewhere describing insecure people or people who deal with stuff like this with hurtful words. It’s not the insecurity or the RSD that makes someone directly a bad partner - it’s how they deal with it and communicate about it. Demonizing insecure people to feel like they’re bad partners is terrible, because the only way for someone with RSD or a lot of insecurities to get better at relationships is to take responsibility for their actions and thoughts and to try and self-explore and become more self-aware - something that is very difficult for insecure people to begin with and telling them that they’ll never be good partners because they are insecure kills any motivation they could’ve possibly had to get better.
When I told my mom about RSD, she started uncontrollably sobbing at a public place explaining that for 50 years she has felt like she’s somehow less of a human being and how terrible it has been for her as well to have to excuse herself from situations to cry because of one comment and how this has made people think about her as someone who always ruins the mood and acts off. She had no idea, for 50 years, why words affect her that much and has felt like a bad mother, a bad friend, and a bad wife. But she had no idea how to stop it, how to fix it, how to do anything about it because she had no idea what was causing it - leading her to believe that this is just the person she is, bad for others. Which, as you might guess, leads to a lot of insecurity and then being told that insecure people are just bad partners creates a loop that is very difficult to start looking at objectively.
TL;DR: Insecurity does not make a person a bad partner or deserving of being called hurtful things. What makes a person a bad partner is insecurity that they have not learned to be self-aware of and to communicate in a healthy way without blame, forcing others to walk on eggshells. And when you make a person feel like they are just a bad partner because of their insecurity, it creates a negative feedback loop that is very hard for them to break out of and start looking at their insecurity objectively and seek out ways to be a better partner.