Question: In the climatic battle of [**The Avengers**](http://www.imdb.com/title/tt0848228/), we see the full might of our heroes teaming up to protect the world. 

However, [**one scene**](http://24.media.tumblr.com/03d89ab3fe7b118238963319b30994e8/tumblr_mmswbjHqd41r1mr1po1_500.gif) during this battle, while hilarious on it's own right, does not make much sense to me.

While battling the Chitauri together, Thor and Hulk eliminate what appears to be a small force residing in a building. While catching their breath, Hulk all of a sudden *punches Thor with great force away from him*. 

But **why** does he do this?

The theories swirling in my head point to either a *revenge* punch for their fight in the Helicarrier. Or a *brofist* for beating a pack of Chitauri, taken a bit too far.

Is there any official wording on why this happened and Thor seemed to think *nothing* of it?

Answer: 
It was obviously a case of Hulk having the last laugh, so to speak and was intended to make people smile or laugh.

I highly doubt that there is any "official" reasoning available for such a minor thing which is clearly intended for the viewers to make what they will of it, with the implication that it was in relation to their (Hulk & Thor's) earlier battle with one another.
That's just a bit of character development actually. They want people to like Hulk so they're showing that he actually has a personality and a sense of humor (though a wicked one) and can show respect to a compatriot, in his own unique way of course. Gleefully arm-punching a buddy he's learned to respect and just fought shoulder to shoulder with shows that he's growing as a person.