Rabe is an excellent playwright -- I'll have to check this out. Movies adapted from stage plays are great places to find good dialog, in general. Other examples: A Thousand Clowns, Angels in America.
I think this might be a reply to a different comment (about Hurlyburly maybe?). The screenplay for Glengarry Glen Ross was written by David Mamet (another excellent playwright, btw), adapted from his play of the same name.