Now, while I haven't watched the TV series in over a decade, so maybe there's something I missed about her story that's changed, I have to say this: Tsundere Harley Quinn is a deliberate disregard for/total failure to understand her character.
She's, to attribute to her what was said about Satsuki from Tsukihime, "in love with love." (In fact, far more so than Satsuki.) Her severe ego issues mean she cannot act in her own self-interest, and has to act in the name of some great love she serves. Her need to serve love and be loved is her defining character trait.
Tsundere behavior is supposed to represent (an often tomboyish) girl who is unready for something so feminine as being in love.
Being a tsundere is as far opposite Harely's core character traits as one could get.
Her relationship with the Joker always struck me more as that of a little girl seeking approval from an abusive and neglectful father than anything romantic.
NWSiaCB said: Her relationship with the Joker always struck me more as that of a little girl seeking approval from an abusive and neglectful father than anything romantic.
Well at least the J Man realizes that.
Harley was like a precocious lovestruck teenage girl who, if pushed far enough, is capable of being much more vicious than her father ever would.