oo do you have examples of issues that very clearly show jokers avoidant attachment style? I would guess on some level the ending of death of the family?
Well, I said that both him and Bruce rather fit the disorganized attachment style, which is also known as fearful-avoidant-- but Bruce has more "fearful", Joker has more "avoidant".
Bruce, despite all his misgivings, has multiple long-term meaningful relationships. But in Joker's case... intimacy and affection are simply out of the question. Humanity is out of the question, like in the example you've given with Death of the Family. The only person we know for sure he cares about is Bruce, and even in Bruce's case he wildly fluctuates between declaring undying love and genuinely trying to murder him out of spite and resentment. The second closest person to him would be Harley Quinn, and I do think on some level he cared about her, but his relationship with her was manipulative and abusive-- and he tried to kill her too. All of his relationships, outside of the one with Batman, are shallow, and it's because he keeps them shallow. People are something to kill, use, or make fun of, not persons to connect with. If there's any sign of emotion, Joker considers it a weakness. Caring gets you broken above a vat of acid at ACE Chemical factory, with a bat from hell scaring you into committing suicide.
Though I don't think Joker started out so avoidant, much like Bruce... who also started out as something else. Personally I see Bruce as having had an anxious/fearful attachment style prior to his parents' death. But then the loss pushed him into avoidance, and ultimately resulted in him displaying a disorganized or fearful-avoidant attachment style as an adult. Joker might've been fearful-avoidant to begin with, if we go by the likeliest background for him: growing up with abusive parents, then living in orphanages and foster homes, etc. Even the one interaction (remembered reliably or unreliably) with Jeannie in The Killing Joke points to a fearful-avoidant attachment:
Batman: The Killing Joke
He's blowing up at Jeannie, projecting his own self-hatred on her, and then immediately swings into begging for forgiveness. In the end, the core thing about disorganized attachment is... instability. Growing up, the child does not feel like their caregiver is reliable, there to provide food or shelter or the most basic emotional validation. Parents who fluctuate between moments of love and affection and moments of violence and abuse teach their children that love is a minefield. One wrong step, and the landmine blows-- and you never know what sets it off, so you wildly overcompensate or avoid. And Jack acts more like this towards Jeannie: he explodes with anger, gets scared she'll react badly, and then begs for forgiveness. It's also clear that he thinks his value is based in what he can provide. If he doesn't have anything to give Jeannie, will she still love him?
But where Jack was more classically fearful-avoidant, Joker is a lot more avoidant. Even though his life-defining trauma happened as an adult, it profoundly affected his view on the world. As Joker, he still has a need for connection (otherwise we wouldn't have Batjokes)-- but he also hates it and is actively trying to snuff it out. It's a bit ironic that essentially, only with Bruce is where the fearful/anxious part of his attachment style still comes out. Just like with Jeannie in that example, we constantly see him go between "It's your fault I became a monster! I hate your guts and I want you dead!" and "I do all this because I love you! I'm the only one who understands you! Please don't leave me!"