What does Mayella really mean in her final statement to the jury in Harper Lee's To Kill a Mockingbird?

During her testimony in Chapter 18 of Harper Lee's To Kill a Mockingbird, Mayella makes several different claims in her final statement to Atticus, the judge, and the jury.

First, it has become very clear to Mayella that Atticus's cross-examination has uncovered all of the holes in her story. One hole is that Tom Robinson is crippled in his left arm and hand, whereas Mayella had been bruised in her right eye, which only a left-handed man would have been capable of. As soon as she sees the flaw in testifying, contrary to Sheriff Tate's testimony, that Robinson had bruised her "left eye with his right fist," she gives the ridiculous argument, "I ducked and it--it glanced" (Ch. 18). A second hole in her story Atticus uncovers is that, though Mayella doesn't dare fully admit it, her father is abusive, as well as left-handed, making him the most likely suspect of abuse, not Robinson. Yet, Mayella, knowing she must defend herself against her father's wrath, sees she must stick to her story of Robinson abusing her; therefore, one thing she says in her final statement is, "That nigger yonder took advantage of me," which she means very literally even though she is lying.

She next makes the following claim in her final statement:

[I]f you fine fancy gentlemen don't wanta do nothin' about it then you're all yellow stikin' cowards, stinkin' cowards, the lot of you.

The word yellow can be used idiomatically to mean being to mean being "cowardly"; therefore, Mayella is calling Atticus, Judge Taylor, and the jury members cowardly if they refuse to convict Robinson (McGraw-Hill Dictionary of American Idioms and Phrasal Verbs). The irony is that Mayella is truly the one being cowardly for refusing to speak the truth and have her father indicted rather than Robinson.

Finally, she declares to Atticus, "Your fancy airs don't come to nothin'--your ma'amin' and Miss Mayellerin' don't come to nothin', Mr. Finch--." By this statement, she is saying that his educated displays of civility don't amount to anything if he is a coward. But, again, the irony is that she herself is the one who is cowardly due to the fact that she has never been treated civilly her whole life and has no education to help her make better judgements.

Hence, though she appears to be insulting Atticus and the rest of the court in her final statement, ironically, everything she says actually applies to herself.