It is first heard in the episode Billy's Achilles, where Billy is singing it to try and cheer himself up. For the backing instrumental, Spencer Wright plays the drums, Rajeev plays an alphorn, and Shanilla messes with the audio mixing.
I’m looking at the bro in the mirror
I’m telling him not [to] change a thing, yeah
No way it will be any clearer
When it comes to being bromazing
He’s the king