세상에 뭐 이런 단어가 다 있어. 제주도도 아니고 제준이형도 아니고. 

From Oxford dictionary @ mac os x

jejune |jiˈjoōn|

adjective

1. naive, simplistic, and superficial : their entirely predictable and usually jejune opinions.
2. (of ideas or writings) dry and uninteresting : the poem seems to me rather jejune.

ORIGIN early 17th cent.: from Latin jejunus ‘fasting, barren.’ The original sense was [without food,] hence [not intellectually nourishing.] 

from naver사전

je・june  a. 《문어》

1. a 영양분이 적은[낮은]
   b <땅이> 불모의, 메마른(barren)
2. 무미건조한(dry), 재미없는
3. 《미》 미숙한, 유치한(childish)

jejune・ly ad. jejune・ness n.

그러니까 without food면 유치하다는 이야기.