Ds2 does naughty things. He tips juice onto his protesting brother's head, he pulls the cat's tail, he rips pages out of books. Naughty things.
I tell him that these things are naughty things to do, and it makes mummy sad when books get ripped, or ds1 sad when heads get wet, or cats sad when tails get pulled.
To which he replies "Yes. I am naughty!" with a look of clear glee and satisfaction.
He is 2.8, how would you deal with this?