What examples illustrate Mayella Ewell as both disgusting and pathetic in To Kill a Mockingbird?

    I agree that Mayella Ewell is both disgusting and pathetic in Harper Lee's novel, To Kill a Mockingbird, but since the previous answerer covered her pitiable side, I will concentrate on her more disgusting nature.
    The fact that she has wrongfully accused Tom Robinson of a capital crime allows her no pity in my eyes. Although Mayella has grown up in a terrible household climate where she has had to serve as a mother figure to her younger siblings, there can be no excuse for the offense she has made against Tom. Tom answers her call for assistance--actually, it is to ease her extreme loneliness--because he "felt sorry for her," a social error that he regrets admitting on the witness stand. In return, she attempts to seduce her unwilling--and happily married--victim; Mayella then concocts a lie against him in order to protect her from her father's further abuse.

    "All right. He choked you, then he hit you, then he raped you. That right?"
    "It most certainly is... That nigger yonder took advantage of me..."

We also find that she made have had sexual relations with her own father.

    "Do you love your father, Miss Mayella?"
    "Love him, whatcha mean?"
    "I mean, is he good to you, is he easy to get along with?"
    "He does tollable, 'cept when..." Mayella looked at her father... he sat up straight and waited for her to answer. 

In the process, she insults Atticus and the entire court.

    "... if you fine fancy gentlemen don't wanta do nothin' about it, then you're all yellow, stinkin' cowards, the lot of you."

It is a choice that will cost Tom his life and set off further retribution through the hands of her father.
    Yes, she is a sad case and a person to be pitied under her earlier circumstances. But, her lack of courage and her racial corruptness prevail, and thereby negates any deserving compassion.

Sorry, sk123, I disagree with the first statement, so I can't answer that one.

Atticus hates the method of cross-examination he employs with Mayella Ewell, though he understands it is necessary to prove Tom's innocence.  Atticus's use of rapid-fire questions, statements of the simple truth, harsh tone, and reminders of Mayella's testimony when she strays from her original story are effective and aggressive techniques.  Scout makes a statement about knowing her father didn't like using these tactics and points out that Atticus rarely used them.  She also tells the reader that Atticus looked like his stomach hurt after questioning Mayella.

His profound distaste for putting Mayella on the spot as he needed to arises from the fact that he feels sorry for her--this girl of 19 who hasn't been to school in years, has no friends, has to play mother to her 6 siblings, gets beaten by her father, and is so very lonely.  All those traits come out during Atticus's early, gentle questioning.  As he puts her life on display for the courtroom, the tragic circumstances of Mayella's life are bared--a fact that would be embarrassing for her.

When Atticus asks Tom Robinson to stand, the reader is told that his left arm is shriveled and useless.  According to Sheriff Heck Tate's testimony, Mayella's injuries indicate that a left-handed person had beaten and choked her.  Thus, we know that Tom is, indeed, innocent.