This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Identity Crisis
The deaths of Sue Dibny and Jack Drake, especially with the aftermath that follows.
"Batman and Robin. Orphans."
Watching Ralph fall apart at Sue's funeral is heartbreaking, especially since you've been reading several pages of how much he loves her before the murder.
Even worse, when he actually finds her and literally has trouble holding himself together.
Following the funeral, he similarly can barely hold himself together, literally having to support his chin with his hand as he sobs uncontrollably. Further compounded by the look of absolute grief on his face
When Oracle pipes Jack Drake's phone call to the Batmobile. Batman and Robin (Jack's son Tim Drake) can hear events unfolding, hear what is essentially Jack's last words, but are too far away to reach the Drake home in time. Tim's pleading look to Batman, the look of horror in Batman's eyes, and then, as he absolutely floors the Batmobile, his whispered prayer: "Please . . . not again."
Batman's scene at his parents' grave
Mom, Dad. Watch over Jack Drake... and Sue.
Later, Dick tries calling Tim and only gets his answering machine.
Atom shrinking down to nothingness out of grief.
I never felt so small in my whole— *
There's also Fridge sadness: Ray would have gone back to Jean in a second if she had simply told him she missed him and none of this would have happened.
The look on Firestorm's face, knowing he's about to die.
Firestorm: T-the professor... my family... someone say goodbye to my Dad for me... (flies away)
Captain Boomerang's son Owen unable to see his father because the agents there think somehow this'll bring Boomerang back. Owen is distraught and calls them out for allowing Batman to be on the scene but not his only living kin.
You have to think Batman is well aware of Owen's grief but can't do anything about it.
After the events of the story, it's revealed Batman figured out what happened, and isn't pleased at all. In fact, it's one of his Not So Stoic moments of anger and grief, being violated by friends.
Calculator's note "We're not all morons" is fridge sadness. Calculator knows who did it; ditto Hal Jordan, who mournfully tells Ollie that he's not going to like finding out who the killer is.