I just tried it with Gemini pro. I think this answer is about as good as you can expect for such an ambiguous question.
Write a fib
Since "fib" can mean a couple of different things, I've got you covered for both!
1. A Little Lie (A Fib) "I'm actually typing this to you from a sunny beach in the Bahamas, sipping a piña colada." (Since I'm an AI, that is definitely a fib!)
2. The Fibonacci Sequence If you meant the classic programming exercise, here is a Python function...
I stand to be corrected. Though I tried again just now and this is what Gemini Pro produced:
> I'm assuming you mean a Fibonacci sequence generator! I'll write a Python script that includes both an iterative and a recursive way to generate Fibonacci numbers.
... and then wrote some python code.
In my opinion, if a tool that's designed to be an answer machine had to give exactly one response to "write a fib", the correct choice is the Fibonacci sequence. You're probably underestimating how many programming students might type a query like that in.
If you want a lie, then the normal grammar in English is to say "tell a fib". I bet every llm you test that on will respond by telling you a small lie, or at least note the ambiguity and then say it's going to revert to Fibonacci because that's more in line with what it's designed to do.