Conversation at lunch

Here is the conversation that took place yesterday at lunch:

Kennedy: Mom, I know what the "S" word is that we aren't supposed to say

Mom: You do?  Who told you what it was?

Kennedy: My friend (after a long pause) Mom, I know we're not supposed to say the "s" word, but can I just say it to you so you know not to say it as well?

Mom: (I am definitely curious at this point!) Sure, go ahead and tell me

Kennedy: (Whispering) It's "STUPID" we are NOT supposed to say that s word

McGuire: KENNEDY!! You just said the "s" word!  Don't say that!

Mom: You are both right, that is definitely an s word we don't use.