I'm dealing with the same thing here, a sibling pair. They both just laugh when i reprimand them. I've seen them do it with parents too, and they do correct saying that's not funny, etc. time outs are used at things and here and almost always have little effect. Its really frustrating and i feel likes a broken record all day long! at this point I'm thinking its either a personality trait or the parents are actually letting stuff go at home and just telling me otherwise. I've find that the standard one min per year old time out doesn't work for my two, they need longer and have to be completely away from the other kids and me.