Good Morning AV. Hey we are there also with our 4 yr old gr son. Same words too. Along with Silly which in it's self is ok, until he starts to try to correct ME with No Silly Nana! Then them there are fighting words....lol
He has stopped saying them on a regular basis now.
I thought for a while he was getting it from his cousin who is also 4 until July, cause he will say Go way, shut up, leave me alone and Corbin used to cry when Asher would get ugly with him. Long talk with Asher Stopped that nonsense.
I don't tell corbin these are naughty words I tell him he is being ugly to Nana when he says them. Then I do ask him if Nana says Shutup or calls him stupid or idiot. Always No Nana. I have had to bring out the big threat though and that is to wash his mouth out with soap. So far I haven't had to. Our son's lived and didn't die from washing their mouths out. So he won't either.
When he tells me Daddy says Shutup or stupid, I tell him Dad is an adult and I know he shouldn't say those word either, but daddys usually do what they want too. So I talked to my son about it. At first he said Mom I don't say that. I had to tell him ya you do especially when your on the phone with one of your buddies, Corbin can hear what you say. Even if it is innocent in the conversation they pick up your words and how you use them. Like when Corbin walked up to his Papa and said What the H377 ya doing Papa!! He sounded just like You! He finally GOT it!
Kids pick up and say what they hear. We stopped watching Car's every day and there are some cartoons we stopped watching also for the same reason.
Tia (9) and her brother Austin (8) when they were younger were on the stairs playing and they know Nana doesn't like anyone to say Butt, so Tia called Austin a Butthead, Austin said Tiaaaaaa Nana says not to say Butt, so she looked at him and said You Hinnyhead. :)) :))
Whatever you decide to use as discipline keep it up. Whether it's time out or loosing his tokens keep doing it. They finally get the message.
God Bless AV hopefully other Mama's will give you better idea's on this one.
K. Nana of 5