reduce!

gistfile1.clj

(defn reducer
  ;; Removes 5 and the item after it from a sequence.
  [{:keys [flag seq]} item]
  (cond
   flag       {:flag false :seq seq}
   (= item 5) {:flag true :seq seq}
   :else      {:flag false :seq (conj seq item)}))

(:seq (reduce reducer {:flag false :seq []} [1 2 3 4 5 6 7 8 9 10]))

In just about any other functional language you'd use a tuple instead of a map. Maps make what the two values are more explicit though so I like them more.

(defn reducer
  ;; Removes 5 and the item after it from a sequence.
  [[flag seq] item]
  (cond
   flag       [false seq]
   (= item 5) [true seq]
   :else      [false (conj seq item)]))

(:seq (reduce reducer [false []] [1 2 3 4 5 6 7 8 9 10]))