I don't remember the exact context, but long story short:
This girl, Sakurako, is completely flat-chested while her best friend is gifted by the gods in the chest volume department, and she's none too happy about it. She's pretty much constantly angry at her friend for having larger breasts than her to the point where she can get a little melodramatic.
Do keep in mind that he’ll be driving a shitbox and not a Red Bull.