Is It True?

My girlfriend has a best friend to whom she tells everything. The other day, my partner admitted that she also leaks details of our sex-life, particularly the generous size and unique feel of my penis (so my girlfriend insists).
Ever since, whenever I see this friend, I can't help but wonder about her thoughts, whether she's curious.
My fantasy is that one day, while she's visiting us at home, curiosity gets the better of her. She asks "is it true?", and my girlfriend insists that I show her.
When she sees it, I imagine her dropped jaw.
Then, my girlfriend insists that she 'gives it a go'.
And her friend just cant help herself.