You must forgive me for saying this, but your question is a little dumb, because how is the client to know if the user is making a mistake clicking the radio button. Equally, people who are not making a mistake will be annoyed/confused by the contrary nature of the button. Anyway, you can achieve the desired effect:
Private i As Integer = 0
Private Sub RadioButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButton1.Click
If i = 0 Then
RadioButton1.Checked = False
i += 1
Else
i = 0
Return
End If
End Sub
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