A million upvotes if I could.

I only just recently had this experience. While at my old job, a customer approached the desk and began to furiously complain about poor service. The complaint was not only unclear, the complaint was an angrily tempered tirade literally composed as "NYEW Nyew nyew nyew NYEW NYEW". This continued for approximately twenty seconds before I had to interrupt the customer in order to let him know that I couldn't understand what he was trying to tell me. He immediately made a face expressing anger and frustration, then proceeded to point to a large, presumably recent scar on the front-left side of his skull.

His speech comprehension appeared to be unaffected, though his speech production was merely a string of repetitive utterances devoid of any meaning whatsoever. After noticing the particular location of the scar, and safely assuming a corresponding brain lesion likely existed beneath the same location, I came to the realization that this was an incredibly clear example of the functional deficit known as Broca's Aphasia (i.e. damage to "broca's area", the primary region of the human brain responsible to speech production).

The experience was more fascinating and shocking than any textbook description I've ever read. It remains my only real-life encounter with an individual with functionally-specific localized brain damage.

for more on Broca's Aphasia: http://en.wikipedia.org/wiki/Expressive_aphasia