The comment has come after he has realised his mistake in one of the sequences in 2005 Black, in which he played a teacher called Debraj Sahay.
A few days back, the 70-year-old had asked the audience about the mistake that he did in the film directed by Sanjay Leela Bhansali.
"...I was asking about the fault in my performance, in that scene, and not the other factors. And here is what the fault was," Amitabh posted on his blog srbachchan.tumblr.com.
Black revolves around a blind and deaf girl, played by Rani Mukerji, and her relationship with Sahay, her teacher, who later develops Alzheimer's.
Sharing the mistake, he posted: "When I inform all at the table that Rani had dictated a letter to me to be read at the table, especially for her sister, whom it was believed she was jealous of, I took out the letter to read, and then my hand went straight to my upper pocket of the jacket to pull out the glasses to read... Mistake."
"I needed to feel around in my other pockets to ascertain where my glasses were, instead of my hand directly going to the pocket. For someone who is soon getting into the symptoms of Alzheimer's, where patients forget where and what they do, it was incorrect of me to go straight to my pocket," he posted.
Even after eight years, he doesn't seem to have got over that mistake.
"Aah! still cringe every time I think of the mistake, or see it on replays! Damn! I am such a rotten actor," posted Big B.