(I don't own the Angry Marines, I'm writing this blog for non-canon reasons.)
Angry Marines are non-canon Chapter who are shown to be very angry and foul mouthed.
The Angry Marines are basically a meme from 4chan as an extreme Space Marine chapter, most pictures show the using "non-conventional" weapons such as a rocket launcher that launches Angry Marines. Angry Marines are represented holding their middle finger and violent.
Their banner is usually an angry yellow face with swear words and other words on it or it is the "This is Sparta!!!" Meme.
They appear in the Dark Crusade mod "Firestorm over Kronus.