I think "stupid" and other putdowns are totally different, so I ak them how they would fee if someone said said hurtful to them such as...this or that. And they get that.

I don't care if my kids say goofy stuff...around the house...and only for a few minutes per day. LOL

My kids were on this thing where whenever one would say something, the other would respond with "chicken" or "jump out the window" and then they would both crack up.

Constantly...grrrrrr

So I would just tell them, "go ahead and laugh...you have three more minutes of this." LOL
3b (with 3c tendencies) on modified CG