I loved this post from Laura at High Rankings yesterday. Brilliant stuff:

How to talk SEO to a CEO
Talk numbers, money, traffic. Show pretty graphs. Steer clear of tech talk.
Attire: suit
Say: “Looking at last years’ numbers, if we implement SEO to this subsection of the site, we can drive traffic up at least 15%, which means a possible $8,000 a day more than 2005.”

How to talk SEO to a Project/Product Manager
Tell them how much easier life will be with SEO:
Attire: business casual
Say: “If we implement SEO into the production process, there will be less SEO-checklists to check at the beginning of every project and there will be less time spent after every project checking how (and if) our SEO efforts were done."

I think she's right on the money with these (there's a total of 5). To her list, I'd add:

How to talk SEO with a Small/Mid-Size Business Owner
Talk ROI, engage them about their specific business, don't use industry buzzwords (like SERPs) and focus as specifically as possible on their industry and their business
Attire: Suit, no tie
Say: "Your firm is currently offering the best products and services in this niche sector and SEO will allow you to reach customers who want exactly what you sell."

Any others. I'm still trying to figure out how to explain SEO to family members and friends at parties. It always starts with - "Ever use Google?"