(defvar my-vandusen-paste-re
  (rx bol
      "<vandusen> \"" (group (+ any))
      "\" pasted \"" (group (+ any))
      "\" " (group (+ any))
      eol))

(defun my-report-spam ()
  (interactive)
  (save-excursion
    (re-search-backward my-vandusen-paste-re nil t))
  (let ((url (match-string 3)))
    (when url
      (let ((id (cadr (split-string url "paste\\?id="))))
        (insert "vandusen: spam " id)))))

;; usage: use M-x my-report-spam in an IRC buffer, then hit RET