Famous Last Words

Don't worry. It doesn't mean I'm about to come up with some famous last words.

That is the good news.

Meaning
Basically, it's a comeback for when someone says something that might well tempt (or bait) fate!

Well, that's it's idomatic meaning.

Use in Normal Speech
When warning of possible trouble.

"I know that's what they want to happen, but they should be realistic...what they're saying could well be famous last words!"