Kotoishi Naru keeps on calling the main character a Junon Boy. He seems to take this as insulting.
What is a Junon Boy and why does he dislike being called that?
Junon is a monthly Japanese fashion magazine primarily directed towards teenage girls and women. It began circulation in June 1973.
Source: Wikipedia
Given Junon super boy contest is a beauty contest I would guess, "Junon Boy" basically means "pretty boy".
The magazine hope page can be found at: http://www.junon-boy.jp/
I am basing my answer on research so perhaps some one else can confirm this, also I could not find any information of the meaning of maganize name alone, so again I am basing on the circumstances.
Someone replied about Junon Boy on Yahoo! Answers 5 years ago. Hope this helps a little bit.
It is a beauty contest for young boys, like teenage boys. Junon is a magazine, like Seventeen. I don't know what they win, but I think many girls' readers vote, and I believe the winner will get some money and a contract with some actor/modeling agency.
Most of the contestants are just young boys who want to be actors/models.