Momma? Is this a bad word?

I have three kids. My oldest child, a spunky 4 year old, has been experimenting with bad words. He always asks me first if they are indeed bad. "Momma, is this a bad word...stupid." I try my best to respond in a manner that won't intice him to continue using said word. After picking him up from pre-school the other day he said that he learned some new words at school, or should I say at the large bacterially infected petri dish? The school my son attends doesn't really buy into the whole discipline thing, they look at childhood as one big learning experiment, so basically anything goes, sometimes great sometimes really bad. So back to the new word. I am driving my car nice and straight along the road, my three little angels sitting innocently in their car seats, and I hear "Momma is this a bad word?" followed by a loooong pause. I wait. He speaks. "Stupid fucker." I was NOT prepared for that!! So what do I do? I , the mom, starts laughing, uncontrollably. Did my son just drop the F-bomb? And did I laugh? Now what....how do I redeem my status as Momma?
"Does it feel like a bad word? Why don't YOU try teaching your friends at school some new words?"
"You mean like Saturn or Jupiter?" says Pele*
"Yes, those are some great words," says the relieved Momma.


*names have been changed- and yes my son loves soccer