;;; It is the opposite of fill-paragraph    
(defun unfill-paragraph ()
  "Takes a multi-line paragraph and makes it into a single line of text."
  (interactive)
  (let ((fill-column (point-max)))
    (fill-paragraph nil)))

And to bind it to a key:

;; Handy key definition
(define-key global-map "\M-Q" 'unfill-paragraph)

Very useful for stuff like whitespace-mode or auto-fill-mode:

(hook 'c-mode-hook (lambda () (xxxxxxxx-mode -1)))
(add-hook 'js-mode-hook (lambda () (xxxxxxxx-mode -1)))