You're not wrong Walter, you're just an asshole

Is this like how I used to introduce my first ex wife to people as "My First Wife" while we were still very much married?

For some reason she did not find it as amusing as I did? I wonder if its funny now?

I like my wife too much to make jokes like that. That's kind of awful, really.

But why would your wife say "it's very disrespectful to refer to them that way"? That doesn't make sense either

It already doesn't make grammatical sense because your wife hasn't died, so you can't refer to it happening in the past tense - you'd have to say "before my wife dies" which ruins the joke.

You could fix this joke by instead saying "before my wife's death" or "before the death of my wife", and having her just say "that's very disrespectful".