Private Sub Worksheet_Change(ByVal Target As Range)
Set Target = Intersect(Target, [A:B], UsedRange)
If Target Is Nothing Then Exit Sub
For Each Target In Intersect(Target.EntireRow, [C:C]) 'si entrées multiples (copier-coller)
If UCase(Target) = "OUI" Then
Application.EnableEvents = False 'désactive les évènements
Application.Undo 'annule l'entrée
Application.EnableEvents = True 'réactive les évènements
Target.Select
Exit For
End If
Next
End Sub