Negative Self Talk

My 7 year old boy will often talk about what a loser he is or how he should be abandoned or doesn't deserve to be alive. The expressions he uses seem to be mimicked rather than his own words so I spoke to his teacher about it and she said it is usually kids with older siblings who bring these phrases into the classroom.

This almost always happens when he has misbehaved so I have considered that he may just been trying to cut off a correction by doing his own version of a correction or just saying something jarring.