I wrote a response last night and then didn't submit. I see this morning, though, that Lynn has said all the things I wanted to say, but better than I did.
I do think that what some are calling "dumbing down" can really be part of social or interpersonal intelligence. Surely we all know there are different kinds of intelligence? Someone who can write a brilliant novel or play may be crap at computer programming. Someone who is a great mathematician or mechanical engineer may be horrible at diplomacy or music. Maybe if you're one of those people who feel like you are constantly dumbing yourself down when talking to others you could reframe the scenario as practicing your skills in interpersonal intelligence.
I stress to my kids that different people are good at different things. I think a lot of times in school settings since there is such a big emphasis placed on academic performance that kids and adults can lose sight of the importance of interpersonal skills and just plain being a good friend. In many cases excellent interpersonal skills are going to take you further than academic skills— the old "it's who you know" adage. And certainly the combo of great interpersonal skills plus excellent academic performance is going to enable anyone to succeed more easily. If you're incredibly intelligent, but a jerk, no one is going to want to hire you or work for you. If you're incredibly intelligent and incredibly kind and caring everyone is going to be clamoring to work with you.
It's really disturbing to me that some of you had the experience in school where you had to act like you were not as smart as you are to fit in. It was never uncool to be smart in my childhood (which was probably longer ago than your childhood since I'm one of the older moms here on MDC) or now. Being nerdy and geeky and awkward and socially inept, sure, that was uncool, but getting good grades and turning in your test quickly—no, that was never a problem. The town I grew up in is not particularly "smart" in any sense of the word, but being one of the smart kids in school is probably the only thing that kept me from being a total social outcast. Smart kids were fairly popular (though not cheerleader level status or anything) and pretty well respected. A higher degree of socially ineptness was tolerated if you were also smart, which probably saved me from total dorkdom. My parents also valued intelligence, but didn't push us at all. I recently went to my niece's high school graduation and she was one of 40+ valedictorians (all had 4.0 or better GPAs) which seems to speak to good grades, at least, not being a barrier to fitting in any more.
I guess it really depends on the circle you find yourself in and/or create around yourself. If you're in a high school environment where intelligence and academic achievement is admired then the whole "dumbing down" thing doesn't come into play. Likewise as an adult if the circles you're in value intelligence (careers in academia, tech fields, medical, etc or just an area of the country with a lotta smart people) then using big words in conversation doesn't necessarily make you look pretentious.
I'm really sorry that some of y'all feel like you have to not act smart to fit in. Here in my neck of the woods, I'm just struggling to follow along with what all the really smart, hard working (that's the key) people are doing. People here are making so much amazing stuff happen that I just feel like a bump on a log and like I have wasted so much time, but I'm just not that driven (or else I wouldn't be wasting my time posting here).