This question presupposes the critical opinion that Othello, the Moor, is essentially deceiving Venice's society with the similitude of nobility and heroism. This theory holds that as Iago provokes him and manipulates him, Othello's posture of nobility drops off and exposes his true diabolical nature. This view holds that as Othello's language changes while he becomes more and more enraged over what he supposes is evidence of Desdemona's betrayal, he associates himself more and more closely with his true diabolical nature.
In keeping with this critical opinion, Othello's deception encompasses all of Venice as he represents himself as one who is more than equal with the noble natures of ethnic Venetians.
And say besides, that in Aleppo once,
... a malignant and turban'd Turk
Beat a Venetian and traduc'd the state,
His self-deception would then be his belief that he is worthy of the honor they give him and that his rage over what he is told by Iago of Desdemona is unique to unique circumstances (instead of his true nature).
It is a bit easier to see Miss Brill's deceptions, mostly because part of it is so pointedly declared at the end of the story. Her deception is that she pretends to be engaged completely in the concert while she, in fact, is also eavesdropping on those around her and vicariously participating in their lives:
Miss Brill always looked forward to the conversation. She had become really quite expert, she thought, at listening as though she didn't listen, at sitting in other people's lives just for a minute while they talked round her.
Miss Brill attends the Sunday concert in the park all year round since she is familiar with the conductor's varying habits in season and out. She is always happy to be there among the other listeners whom she regards as acquaintances. Her self-deception is that the others are as interested in her and in their shared experience in the park--as fellow actors in a play--as she is in them.