If you are dealing with a disrespectful grown child, here are some ways how you could respond to their cranky, unreasonable behavior:
Try to understand them instead of ignoring the red flags
Do not threaten them or yell at them
Offer them logical explanations to things they crib about
Allow them to be on their own and to take a breather
Respect their boundaries
Ask them if they'd like professional help from a therapist
Show them all the love, care, and affection you can - even when you may just want to yell at them for being so hurtful and disrespectful towards you