The word "meh", originated from an episode of "The Simpsons", has officially been entered into Collins English Dictionary. http://news.yahoo.com/s/ap/20081117/ap_on_re_eu/eu_britain_new_word
I realize The Simpsons probably popularized it, but I'm 50000000% sure people have been saying that for hundreds of years.
In all truthiness, I don't think Stephen Colbert would care if someone said Meh wasn't an actual word. You only say that because you read it in a book. In my gut, I feel like meh is a word, along with huh and hmm and flkfgjlkgjslf.