I know there's probably a way to do that using regex, but I can't quite seem to figure out regex in vim. I tried searching: /-\{2} but it catches triple hyphens, too.
I also can't just do a traditional find and replace, since I have triple hyphens in my file. Searching for -- returns triple hyphens in addition to double hyphens.
:%s/--/---/g? It works for me. – Tomer Vromen Feb 18 '12 at 23:27