I'm not sure if flexing is the right characterization, although it is effective as a comical reference. It is derived from the body building scene where flexing without any degree of defined muscle would be very obviously seen as ridiculous. In the music scene, they call this posing. I believe that is indicative of someone that dresses like a rockstar but can't carry a tune let alone write any sort of smash hit song. I'm sure there are various other cultural examples to reference, and similarly the devil poses as an angel of light but, when I offer my view, I try only to do just that, not expecting anyone to see it as a masterpiece and surer that there will be critics but, personally, I do believe I'm making a beautiful sound.