From a circa-1970's issue of Reader's Digest, Quotable Quotes (I remember this because my mom had it taped to the inside of the pantry door for a decade or two):

If you really want the last word in an argument, try saying "I guess you're right"

and guess what... it works! =)

and in reckless deviation from the subject at hand, i might as well share the quote which she had taped below that one, only because i think it's so wise (and could potentionally be put to use here in AWADtalk, in these volatile times):

"Never answer an angry word with an angry word... It's the second one that makes the quarrel"