Lets go over the definitions.
Denotative meaning refers to the meaning of a word as it can be found in a dictionary; it is a form of literal meaning.
Figurative language means that the words imply something else than their dictionary meaning, either through connotation or similes etc.
Verbal irony means sarcasm through words, not just your voice.
Dialect refers to a version of language that has some forms that differ from the most commonly used forms; it is an idiom.
It is apparent that given the above definitions and the rarity of the phrase Yeb'm (Yes, madam) we have that it is an example of dialect.