This is the 1955 short story "Judgement Day" by L. Sprague de Camp. It was released in The Best of L. Sprague de Camp in 1978 as well as in Great Science-Fiction in 1965.
The scientist muses about his life and how everyone was always mean to him, and then decides to release the research about how to cause iron to explode atomically anyway. You have remembered it well, all the details you mention are straight out of the story.
A scientist who has developed a new type of nuclear weapon. The technique is so simple but devastating that he is sure if he releases his work, all humanity will be destroyed.
The narrative is told in the first person as an interior monologue of the narrator. Physicist Wade Ormont has serendipitously stumbled on a hitherto unsuspected variety of nuclear fission involving iron that could "blow the entire crust [of the world] off with one big poof," a discovery he agonizes on whether to report. [...]
There is powerful reason for him to maintain his silence. His discovery would make production of a weapon based on its principles so easy as to render universal holocaust inevitable, as at some point some petty country would be bound to engage in nuclear blackmail and destroy the world. In effect, Ormond holds the fate of mankind in his hands.
Wikipedia, Judgment Day (short story)
He reflects back on his life, revealing he was a genius at an early age and brutally bullied and beaten by classmates. He was nicknamed "Sally" which crushes his confidence around women later in life (he mentions he couldn't even date a woman named Sally as an adult).
Ruminating over his choice, Ormont reflects on his past life. A weakling and loner, he had grown up bullied and abused by his peers despite, or perhaps because of, his brilliance. As a result, he became a friendless loner and outcast, so deficient in social skills even his wife eventually left him. He now cares so little for his fellow human beings that their future and his own short-term self-interest seem evenly balanced in his mind. After all, he would most likely be dead of natural causes before some lunatic blew up the Earth.
He ends the story by saying "I would kill you all slowly if I could" and reveals his work to the world.
It is actions of a group of young neighborhood delinquents that tips the balance. After they maliciously vandalize his house, Ormont comes to the realization that he truly hates the human race, and these examples of it in particular, and can only be happy if they are made to pay. Publication would thus be an act of ultimate vengeance for all he has suffered, and on all who have made him suffer. He decides to write his report.
Also the answer to this question: Short story where a scientist finds a way to explode the iron in the Earth's crust, considers a childhood of bullying, and releases the process