Normally, saying someone is “not the man I married” means that you, for example, married someone who was ambitious, but now he’s lazy. Here, instead, she’s realized that the person she’s living with is literally not the person whom she married. It’s funny because normally you’d think a person would be able to tell this just be looking, but she has to consult the marriage certificate.
I think the joke is that she’s using the phrase in the usual sense, but sarcastically literalizing it.
Slightly similar: Older couple on a couch. The man has just pulled a rabbit out of a top hat and is saying, “There. I’ve restored the magic to our marriage.”
But if they married young, then she would be just as upset about it if he were still the same guy she married and she’s had personal growth.
Comics I Don't Understand 
Normally, saying someone is “not the man I married” means that you, for example, married someone who was ambitious, but now he’s lazy. Here, instead, she’s realized that the person she’s living with is literally not the person whom she married. It’s funny because normally you’d think a person would be able to tell this just be looking, but she has to consult the marriage certificate.
I think the joke is that she’s using the phrase in the usual sense, but sarcastically literalizing it.
Slightly similar: Older couple on a couch. The man has just pulled a rabbit out of a top hat and is saying, “There. I’ve restored the magic to our marriage.”
But if they married young, then she would be just as upset about it if he were still the same guy she married and she’s had personal growth.