The language used in this expression is pretty straightforward, so it won't require a lot of explanation. However, people will often just say the first part and leave off the second part. It's also common to put Well in front of it to make it sound more categorical.
Well if that wasn't the most boring movie!
Bobby: Remember this one?
Boris: <gasp> How could I forget! My sixteenth birthday and that awful little mustache.
Bobby: And this is my Angie's wedding picture...
Boris: If she wasn't the most beautiful bride, (I don't know who was!)
Dude, if that ain't a fake, I don't know what is!
In this meme, the commenter below identifies completely with first person in the meme: I like you, but I can't get into a relationship right now. Note that they say I don't know what is, but you can also say who is.
Again, the nuance here is: Yep, that's definitely me!
The men in this meme are from the series Outlander, in which they're arch enemies. The first man, Jamie, asks the second one if he's ready to fight, and the second man is caught by surprise because he thought he'd never see Jamie again, and yet here he is on the battlefield!
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Let's dance! is street talk for Let's fight!
As you can imagine, intonation is key in all the expressions on this page.
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When we throw people's words back in their faces, we often call men Mr. "[words]", and women Little Miss "[words]".