The Angry Marines are in essence what would likely happen if /tg/ could magically turn themselves into Spess Mehreens and express their opinions towards certain aspects of the canon of 40K. Except they were actually created by some guy using the Dawn of War army painter for the first time in ye olden days of yore. They are not the Alfa Legion and they symbolize rage. Which we have in copious, albeit impotent, amounts.
The Angry Marines are a popular homebrew Chapter of Space Marines, and by far the most famous homebrew to gain fame outside the realm of /tg/. They are angry for the Emprah and skittles. All the time. Angry Marine tactics focus on getting into melee as quickly as possible, and proceeding to bust open several crates of ♥♥♥♥ YOU in the various directions of the Imperium's enemies. Due to this, Angry Marines tend to have low BS (by low, we mean Ork boy low), but have terrifically high WS/S/I, that anyone getting into CQC would be utterly annihilated.
There is even a Codex: ANGRY MARINES detailing the special rules required to adequately represent their rage.
The Angry Marines employ a variety of weapons notably different to the standard Space Marine arsenal. These includes power heavy bolters, for melee use, dual power fists, power feet, power bats, power wrenches, and even the Predator Angrinator, a modified version of the Predator Whirlwind artillery tank that fires the Angry Marines themselves directly into the enemy ranks. They also possess a Titan Legion, which is fully composed of Angry Titans. These are detailed in Codex: ANGRY MARINES. The Angry Marines also think that pistols are for ♥♥♥♥♥♥♥ who can't hit a dam, and so these marines rarely go into battle with the traditional pistol+CCW combo opting instead to engage opponents in mêlée combat.