Vacuum Shock

Vac-combat is not the same as in-atmosphere. Even the lowest grunt on a planetary defense force, who lived in a gravity well their whole life, knows that. One well placed shot to critical life support is a death sentence, condemning the victim to one of a myriad of deaths. Fleshy meat bags were never meant to be out here in space, but we were never going to let that stop us. Nor were we going to let our petty squabbles about 'land' and 'money' stay behind as we left for the vastness of the universe. Even as we found new worlds to explore and conquer, we kept to our old ways of dishing violence unto each other. The manner of killing changed, but the end result always stayed the same.
Hundreds of years ago, some of the first recorded casualties of what we now call 'vacuum shock' met their unfortunate end when their capsule depressurized while preparing for re-entry. The symptoms haven't changed since then, but we have learned much about the consquences. Asphyxiation is the major symptom, that's what emergency hypox blood was made for. A hypox injector can keep the body oxygenated for 2 minutes, long enough to return someone to pressure. The real nasty killer is the vacuum boiling. All the liquid in the body, suddenly liberated of the pressurization from a vac-suit, rapidly vapourizes out of it. It's like 'the bends' on steroids. The rapid depressurization also rips the air right out of your lungs, so if you were holding your breath, you're probably gonna pop a lung or two.
Most aug-head void-jockeys definitely have one up on anybody not mech-ed to the neck. The reduction in blood usage, and the availability of mechanical internal organs mean the only squishy stuff you need to keep oxygenated is the stuff in your skull. A couple different companies make entire void-rigs specifically tuned for cerebral transfer, meaning you could strap your brain into a all-chrome body tuned specifically for void-work, RCS thrusters and everything. Integrated systems clean chemicals from the blood system, oxygenate it, and provide required nutrients to the cerebral 'carapace'. Some even contain their own miniaturized drive packs, allowing the user to move loads significantly larger than themselves. These suits tend to cause the user to suffer from something known as 'integration syndrome' after extended usage, where they feel their missing systems when not connected to the void-rig. Dissociation drug treatments have been tested in an attempt to rehabilitate long-term users, but are still somewhat experimental and thus tightly controlled.
Nowadays, we've figured out most of the ins and outs of killing and dying in space. Point defense tech has developed beyond your standard machine gun, to lasers and plasma field projectors, but chemical weapons will still fire in vacuum, and a slug of metal is still a slug of metal. You might be able to swap 80% of your body with plas-steel and rigi-plex, but if your grey matter gets pasted around the inside of your helmet, it's not going to do you much good. I've seen a man ripped clean in half by a rotary PDC, there's not much a mech-doc can do when you've been scattered to the solar winds. Armor can help, but if you can't move fast enough to avoid laser targeting gimbals, or throw up scatter-screen to dissapate the beam, you're gonna watch as your temperature management system struggles to keep up, cooking you in your suit.
You've got options to get to your enemy that have been developed and refined over the centuries. A long time ago, docking and locking was the preferred method, because we were civilized, and there weren't too many ships, so the loss of even 1 ship that could have been taken instead was a serious strategic consideration. About a hundred years ago DioChemiTech managed to develop void-seal foam. After reports that criminals were using escape pods to ram and breach ships, sealing the gaps with foam to stop venting, military minded thinkers came up with refined breaching pods. Due to the inherent nature of breaching strategy, pods are not heavily armored and usually unarmed aside from the occupants. Various designs for pods exist, from squad sized breacher capsules, to single occupant breaching coffins, which can be fired from EM rail launchers, accelerating up to the limits with which a body can sustain. Worst comes to worst, void-walking to the enemy and hoping you get a mag-lock engaged is always a last resort.
Once you're on an enemy ship and ready to board, you've got another problem. Mag-locks keep you from flying away when the delta-v changes, so you can stick yourself to the side of a ship. Unfortunately, mag-locks overheat with increased strain. As the computer attempts to increase the strength of the field to stay locked on, the magnets heat up, and eventually an override kicks in, unlocking before you cook your own feet with your boots. Any smart pilot is going to start a dump burn or circular burn to try and overload your locks as soon as they realize you're on their hull. This is why it's preferrable to slag their drive if command wants the enemy alive.
All this, and you have to be aware the whole time that the reactor and drive pack in every ship larger than a skiff is a bomb capable of levelling a city center. Every military ship contains a scuttle protocol system, allowing it to be overloaded to prevent capture. By dumping additional fuel into the reactor, and retargeting the fold device to collapse the fuel onto itself, a miniature black hole is created, which promptly collapses and detonates, destroying the ship and surroundings. Sometimes, it's preferrable to die with honour than live as a prisoner or be spaced out an airlock. One might think reactor overload is the last resort of desperate sailors, but after the attacks on the early asteroid warning systems of Ignaxus, we must be prepared for anything. But in the end, the fear of every trooper in space is the knowlege that one shot is all that stands between them and a painful death from vacuum shock.