I have almost the same situation happening in my 5th grade class. I know that I am a good teacher and I work with confidence at all times. I've never allowed this parent to treat me in a disrespecting manner and I've remained civil. However here's what I'm doing to protect myself:
Document, document, document
Never meet with her alone, always have another teacher, EA or Principal with you.
Make your principal aware of what is going on
Keep work samples of her child
However, have a conference with the principal and parent. Let the parent know that passing Kindergarten (or any grade, really) depends on the work her child does. While she may want him to play all day and be undisciplined, that will not be allowed at school...have your principal corroborate you on this. If her child does not work, and is unruly. How does she expect him to learn? Then, finally, make it known that parents always have a choice about where their child learns. If she'd like to try a private school, charter school, or any other school / teacher (if your principal allows) that is also up to her.
Really, all we have to do is put responsibility back where it belongs...with the parent. Education begins at home and we only have these kids for a short amount of time. What does she want? A miracle? We are not miracle workers, and we need a TEAM if we're going to help any child succeed. The mother needs to realize that she's not being a good team player.