This theory comes from Facebook user Philip Johnson.
One night at the Wayne mansion long ago, Martha goes to Thomas' study to tell him it's time for bed and for them to go upstairs. He declines and continues to work, as usual. Frustrated, Martha then goes into the liquor cabinet and begins to drink. She goes to her room closes the door then begins crying. Alfred hears Martha sobbing. Martha begins to tell Alfred she's tired of feeling neglected. Alfred calms her down, and they both begin to drink. One thing leads to another...Alfred wakes up sometime shortly after and returns to his quarters, neither of them tell Thomas to preserve the relationship and the Wayne family name.
10 weeks pass and Martha wakes up feeling sick. She goes to the doctor and finds out she is pregnant. Still in shock, she tells neither Alfred nor Thomas that the Alfred is the father. Thomas and Martha agree that they are not ready to be parents and give the baby boy up for adoption.
The guilt of what she has done plagues Martha. She writes a letter to Alfred explaining everything - that it was Alfred's child she was pregnant with, and how she regrets abandoning him, but she decides not to give him the letter. The child that was given up for adoption has been growing up and living in orphan homes. He causes trouble and displays early signs of psychopathy. No family wants him and he is tormented by the other children. Eventually he goes mad.
Years later, Bruce Wayne is born. Alfred is cleaning and stumbles upon a letter addressed to no one. He opens the letter begins to read. Alfred is furious and resents Martha for lying to him, and for giving up their child whom he would have loved. Alfred's resentment builds, and one night, he decides to follow a Wayne family outing in secret. After the show, they cut down an alleyway and are shot by an unseen figure guised as a robber.
The man who shot the Waynes is none other than Alfred. He keeps Bruce alive so that he knows the pain of growing up parentless, like Alfred's own son, whom he tried and failed to find. In a cruel twist of fate, Batman's two biggest enemies are his own butler, Alfred, and his half-brother, The Joker.
Joker Didn’t Kill Anyone at Bruce’s Fundraiser for a Reason
This theory from Redditor poeir (perhaps more an observation than a fully fledged theory) suggests that Joker crashes Bruce Wayne's fundraiser in The Dark Knight to confirm his belief that Harvey Dent is Batman. He wasn't there to kill anyone, but to unveil Batman's identity. The evidence? Well, firstly, Joker states, “For a minute there, I thought you were Harvey Dent" at one point. Later in the film, Joker toys with Dent when he’s shooting at his convoy; it seems like he's not even really trying to kill him.
Here’s the theory, in all its glory. If you haven't seen The Dark Knight in a while, it might be a little confusing:
"First, when the Joker arrived at Bruce's fundraiser for Harvey Dent, the Joker wasn't randomly killing people--he had a plan, and part of what made his plans horrifying was his ability to tell the police exactly who he was going to kill and then kill them. Killing random bystanders doesn't accomplish that. When the Batman (who the Joker thinks is Harvey Dent) jumps out the window to rescue Rachel, the Joker expects them to be the same person, so there's no reason to keep looking for Harvey Dent at the party.
Later, when Harvey Dent is being transported by police, the Joker uses an escalating series of weapons against the convoy, but doesn't use the rocket launcher on the paddywagon containing Harvey Dent. The only weapons he uses are ones that can't penetrate the paddywagon's armor, and he gradually escalates to make the threat to Harvey Dent seem real. He does this to discover if they really are the same person: If the Batman shows up, Harvey Dent isn't Batman. If the Batman doesn't arrive, Harvey Dent is Batman.The Joker never wanted to kill Batman (he says as much in the interrogation scene, 'I don't, I don't want to kill you! What would I do without you? Go back to ripping off mob dealers? No, no, NO! No. You... you... complete me.'), he wanted to force Batman to break his 'one rule.' A dead Batman cannot be corrupted, so as long as Harvey Dent might be Batman, Dent must not be killed."
Batman Is a Patient at Arkham Asylum
Reddit user slugboy questions whether the death of Bruce Wayne’s parents cracked his mind, leading him to create Batman and the entire Gotham universe in his mind. Alfred, unable to take care of an insane young Bruce, sent him to Arkham Asylum. The people Bruce encountered in the asylum became characters in insane Bruce's Batman drama.
As per this theory:"Alfred would come to visit and attempt to be the voice of reason, but never could really get through. Dr. Jonathan Crane tried various methods to snap Bruce back into reality, but Bruce's reality is so terrifying that he receded back into the delusion. Dr. Edward Nigma, a therapist, would try to reason Bruce back in to the real world, but Bruce would twist his words into riddles. So, he continues to chase these villains and bring them to Arkham Asylum from which they will inevitably escape - because they were never actually incarcerated."
Robin Is a Potential Weapon Against Batman
As comments on this theory point out, the idea that Robin is a safeguard against Batman seems like a genuine plot from a cartoon or comic, one it would be interesting to see in the future. The theory posits that Bruce Wayne himself put Robin in place just in case Batman loses it and becomes a villain.
The theory, from Redditor acidityregulator, states:"What Batman fears more than anything is turning evil. He is perfectly aware he is capable of doing so, and just about no-one would be able to stop him if he was a villain. But what if there was a person who knew his fighting style and weaponry inside out and back to front? What if there was another person with his skill and similar life experiences, yet far more young and optimistic than Batman?"