Greetings, Green Brothers

"REEEEEEE" is an onomatopoeic expression of intense rage or frustration typically associated with the Angry Pepe character and used by those who frequent the /r9k/ board on 4chan. The expression is often associated with the Autistic Screeching meme, however it is intended to represent the unique croak produced by several species of frogs when agitated.

Certain frog species are known to produce a shrill scream noise to ward of predators when threatened. On October 25th, 2009, the earliest known video of this behavior was uploaded by YouTuber ppparaone, which gained over 2.5 million views and 4,600 comments in the next six years (shown below). This video would later one become even more popular with a screenshot of a comment, and spread to humor content aggregator clickbait websites such as Buzzfeed or Smosh