Bad word!

Bedtime conversation:

Me: So what are the things you are grateful for today? Or the weekend in general?
Rod: Hmm... Wala man... None really.
Me: What?! The fact that we were able to go on an outing is...
Forest: (interrupting me in an irate, sleepy, tired voice) Nanay! Sabi mo bawal magsabi ng bad words! (You said, it's not alright to say bad words!
Me: (perplexed and don't know what I said exactly) what? What did I say?
Forest: f**k.

Rod doubled over in laughter.
I was aghast! And asked,  "How come you know that word?!" But explained I said, FACT and what it means exactly.
Rod who was laughing the whole time helped explained as well.

My gas!