DS (4 yo) has for a few weeks been randomly chanting horrible things about his little sister. Like "she smacks her face, she likes to smash her head through glass windows, then throw her in the rubbish bin." It's at no particular time. They could be getting on perfectly well, playing, then suddenly he's saying stuff like this with a smile on his face.
I find this pretty horrific. I'm pretty sure he's doing it for attention, because he's looking at me, so wonder if I should ignore it. But at the same time it's quite horrible and want to pull him up on it and say it's unacceptable.