っての
kitteno

Suffix
Pre-noun Modifier

1. the most ... of all (in team, department, class, etc.); the greatest ... in

Usually Written in Kana
田中 たなかくんは省内 しょうないきっての馬鹿 ばか しゃだよ。
tanakakunwa shōnaikitteno bakamonoda. yo
Young Tanaka is the stupidest person in the department.