buffer-minus.el

(defun buffer-minus (subtrahend)
  "This function takes the name of a buffer, 
  and removes every line in the current buffer present in the given one. 
  The lines are removed with `delete-matching-lines' which uses the given string as a regex
  but it is good enough..."
  (interactive "*b")
  (let ((sub-list
	 (with-current-buffer subtrahend
	   (string-split (buffer-string) "\n" t "[\t ]+"))))
    
    (mapc (lambda (x)
	    (goto-char (point-min))
	    (delete-matching-lines x))
	  sub-list)))