It's too perfect. All three of the people in the conversation had to say just the right things to get to the "punchline". If any one of them had followed a regular conversation path, it wouldn't have worked.

The aunt had to rapid fire questions all the way down to "what's his job" before waiting for a name or any other details. Also, the "What is his job" is suspicious. It's much more normal to ask "What does he do" but then the OP would have had to reply with "she's a florist" and we wouldn't get the desired ending.

The OP had to answer just that one question, ignoring all the other ones.

And the cousin had to set up the punchline perfectly by making a baseless assumption. An assumption, by the way, which is the exact opposite of the rational one given the circumstances (if some chick tells you she's seeing someone and you assume it's a guy, the fact he's in a relationship with a girl makes a pretty damn strong case for him NOT being gay).

Lastly, despite the fact that the idea of the conversation itself is pretty unrealistic, the OP had to one up herself by claiming this is how she came out to her "entire" extended family.

For me, it's always that last dig they have to get in that makes it r/thathappened. It couldn't just be a conversation she had where her aunt assumed she was dating a boy. No, it had to have the "douchey" cousin in there and a snide reveal at the end too.