"You should know better!"

• A bit of chiding
• "You know better than that!"
• "Aren't you ashamed?!"
• "You should really know better!"
• "Shame!"
• 'For shame, for shame!'
• "You shouldn't have done that"
• Disapproving sounds
• "Shame, shame!"

Wiktionary Word definitions in Wiktionary
interj. (alternative spelling of tsk tsk English) vb. (context intransitive rare English) To make a ''tsktsk'' sound of disapproval.