Dumbing down. You read about it a lot. Just the other day, someone told me that a recruiter had mentioned to them that they should 'dumb down' their resume. 

"You use words that are too long and nobody understands what you are talking about."

How sad - particularly since it seems that  there might be a reason.

Of course, if language, vocabulary and and use thereof was one measure of how dumb you might be take note that Wikipedia reports that ....

It has been estimated that the vocabulary of English includes roughly 1 million words (although most linguists would take that estimate with a chunk of salt, and some have said they wouldn't be surprised if it is off the mark by a quarter-million); that tally includes the myriad names of chemicals and other scientific entities. Many of these are so peripheral to common English use that they do not or are not likely to appear even in an unabridged dictionary.
Webster's Third New International Dictionary, Unabridged, together with its 1993 Addenda Section, includes some 470,000 entries. The Oxford English Dictionary, Second Edition, reports that it includes a similar number.

Imagine the problem that we have when 

A Native-level fluency of a language is estimated to be between 20,000–40,000 words, with basic conversational fluency possibly requiring as little as 3,000 words.

i.e. if you use somewhere in the order of 5 to 10% of a language to communicate your written ideas - you are considered fluent.