The expression ‘you know what’ is when one may say to another to get their attention, in a conversation. One may say this expression several times throughout one conversation to ensure they still have the attention of those participating in the conversation.
‘you know what’ also is when your stating to someone about something there not aware of , or when someone constantly pays them out they use the expression.
Your outfit looks like your going clubbing not to work!
‘you know what’ no one likes you!