What is the definition of "hangry"?

Is hangry a real word? According to Collins Dictionary it means to be angry as a result of being hungry, but it seems far-fetched.

If it's in a dictionary, especially one with professional full-time editors, the chances are it's a real word. Of these kind of dictionaries, I can only find it in Collins, and their webpage notes it's "humorous" and also added from a recent suggestion:

Comment byCollins Dictionary (Admin) on 7 Sep 2012
'hangry' definition based on an original suggestion by Jude made on 2012-06-29.

Collins also say:

Word Frequency: No usage level data available

The word is in Urban Dictionary and first defined in 2003. Their most popular definition was an Urban Word of the Day with over 10,000 upvotes so it must be fairly well known slang.

You can find it used on Twitter, although often with an explanation it means hungry and angry.

The earliest hangry I found with this definition in Usenet is in rec.games.trivia from 1996:

[Hangry], although not often used in current English, describes the person who is so hungry he becomes angry. Tell your callers this and they probably won't call back with any other questions.

So it appears to be used as humorous slang, and you should only use it as such.

Edit: It's now been added to Oxford Dictionaries, which adds to its wordocrity.

It is slang, but it's become commonly accepted slang...though not commonly used. According to the Urban Dictionary, it means:

When you are so hungry that your lack of food causes you to become angry, frustrated or both.

An amalgum of hungry and angry invented to describe that feeling when you get when you are out at a restaurant and have been waiting over an hour to get the meal that you have ordered.

I found several other sites which used similar definitions...and in fact, it's the most logical definition I could think of.