He is a really nice boy generally and there have been no changes at home or school, but it has happened a few times now. He will refuse to do something (ex brush his teeth) and shove me and lift up something like a chair, and say 'I'm going to smash your face in' or 'I'm going to destroy the house.' He hasn't done anything, but he has gotten further and further to the point I'm worried at some point he will cause harm. I have no idea where he could have gotten this.
I tell him that's unacceptable and he will have timeout etc. Then he usually bursts into tears and runs into his room until he's calm but is still verbally angry ('leave me alone, I hate you.')
How to react? Consequences and strictness worked when younger but not now.