top banana in the shock department

HollyがJoseと旅行中に寝たのではないかとMagが疑うので、Hollyは "...simply told her I was a dyke" と言ったとHollyがFredに話した直後の場面です。
'She couldn't have belied that.'
'The hell she didn't. Why do you think she went out and bought this army cot? Leave it to me: I'm always top banana in the shock department. Be a darling, darling rub some oil on my back.'
"top banana in the shock department" は中々ユニークな表現ですが辞書で分かるでしょうか？
"top banana" は直ぐに分かりました。
・Wiktionary:
　(idiomatic) The boss, the leader: Only the top banana can make a decision of that magnitude.
　(idiomatic, dated) The principal comedian in a vaudeville or burlesque show.: He was hilarious, and remained the top banana on the tour for years.
問題は "shock department" の方です。辞書には "top banana" と共に使われる例も "shock department" のみの例も見つかりません。しかし、"department" を良く見ると次ぎの用例があります。
・Collins English Dictionary: informal a specialized sphere of knowledge, skill, or activity ⇒ wine-making is my wife's department
・Infoplease Dictionary: a sphere or province of activity, knowledge, or responsibility: Paying the bills is not my department.
"department" は日本語で言うデパートとか組織など以外にも使えるのですね。　それなら "top banana in the shock department" は、「ショックを与えるのが得意」と解釈できそうです。つまり、HollyがMagに自分は "dyke" だとショッキングな暴露をしたと言う事でしょう。