Lol while everyone is right about how bad it sucks to be a Guardsman, no one has really managed to convey just how really effing bad they have it. So allow me to attempt to sum it all up in one post.
Now we all know that the average life expectancy for a regular Guardsman in the illustrious Imperial Guard is approximately 15 hours. But that just doesn't tell the whole story. The real joys are not only in what they have to fight, but their daily existence as a whole.
To start with almost every single Guardsman is in the Guard against his or her will. Be it mandatory drafts as part of their home planets Imperial Tithe, punishment for crimes they committed, or simply plain desperation due to a terrible lot in life, most of the Guard would prefer to be ANYTHING else, save maybe a servitor. They lose all "rights" as an Imperial citizen and therefore have no possible future life other than the Guard. They are in it for the long haul.
Next up comes training. This usually happens on the more hellish parts of the particular Guardsman's home planet, and anyone who knows their fluff can tell you there are MANY worlds out there whos best areas are worse than anything here on earth. Soooo after some hellish training that can and does result in deaths (either through the training itself or execusions of those unwilling to go any further), the unfortunate individual is inducted as a private into the ranks of the Immortal Emporer's Glorious Imperial Guard. To this end his is issued a set of gear that differs on most worlds but commonly includes such items as Flak Armor, a Helmet, and the ubiquitous Lasgun (or Flashlight). This gear is sufficient enough to keep the lucky individual alive when not fighting (most of the time) and allows him to have a percentage chance of scoring at least 1 kill before his horrible death (though some very lucky few can escape from a battle victorious with naught but the lightest of armourments). If the Guardsman is one of the very very lucky and skilled few, he might even earn the honor of being promoted and gaining better gear. Half the time this gear only increases his chance of death due to the fact that his own weapon is likely to kill him (see any plasma weapons). He might even be granted the right to wear armor as advanced as Carapace armor which actually has a slight chance of stopping a single bolter round! (though heavy bolters are still very out of the question). But with rank comes even more danger. The Guardsman who makes sergeant is expected to lead his squad from the front, and keep discipline in the squad. Failure to preform any of these duties to the best of his ability has a very strong chance of seeing him executed by the friendly neighborhood Regimental Commisar via bolt pistol round to the head. So generally, the higher one rises in the ranks, the more likely they are to die.
Also this might be a good place to mention the regulations and punishments of the Imperial Guard. I will start just by listing the offenses punishable by death by shooting: Disrespecting an Officer, Failure to Salute and Officer, Striking an Officer, Failure to Carry Out an Order, Disobeying an Order, Ill-Treatment of Neglect of Accoutrements, Disrespectful Speach Towards the Emporer (flogged then shot), Mutiny, Intoxicated on Duty (flogged then shot), Sleeping on Sentry Duty, Leaving Sentry Duty Without Leave, Cowardice, Inflicting Self Harm (flogged, flayed alive, then shot), Compelling a Surrender, Crimes During Insurrection, Crimes of Fraud Against the Imperium, Desertion. There are many other crimes punishable by such punishments as: Death by Hanging, Being Sent to a Penal Legion, Death by Starvation, and Being Mind Scrubbed and Turned Into a Servitor. Needless to say, NEVER EVER DO ANYTHING WRONG.... EVER.
Now, on to vehicles. Everyone knows the Imperial Guard quite simply has a hard-on for tanks. They field litterally a mind boggling number tanks, of many many different types. The problem is every single one of these tanks is designed along a thought process very similar to American tanks in World War 2. Simply put, field so many that no matter how many you lose, you have enough to win the battle. You lost 90% of your tank core in a battle versus a much smaller force? Huzzah! Another glorious victory for the Imperium! We will have all 900 tanks lost replaced by next tuesday. Being in one of these machines is simply not good. Their armor is light and their weapons strong. All offense, no defense. Which means when one of these babies is hit by an enemy weapon, there is a staggering number of horrible ways to die. Battle Cannon rounds detonating, Heavy Bolter shells cooking off INSIDE the hull, promethium vats going up in flames, Lascannon generators overheating, and Emporer help you if an Earthshaker round goes off anywhere other than FAAAR downrange. In short, their vehicles are NOT a place you ever want to be (although being on foot is probably not any safer).
Moving on we have all of the fun of simply getting to the battle in the first place! So your being deployed to a planet approximately 4 weeks warp travel from here? Cool! Seeing you in 1000 years. Maybe. Or maybe tomorrow. Or maybe never. Your Gellar field could very well fail and all of a sudden the warp is no longer outside your little bubble. I hope you have time to get your pistol to your head and pull the trigger if that happens. Simply put, Warp Travel SUCKS! It sucks for Space Marines so lets multiply that by 100 for your average Guardsman. And lets not forget the dangers of enemy ships. Enormous shipborn Lance weapons tearing your transport into pieces. Fun fun for you!
And finally we can look at the enemies these lucky men and women get to fight. Starting off we will look at the forces usually allied to the Imperial Guard. The Adeptus Astartes, the Space Marines. These enormous, genetically altered, power armor wearing killing machines are death incarnate for a Guardsman. Not only can their basic armor stop anything short of a tank-killing weapon, but their standard issue weapon is an enormous rifle that fires a .75 caliber mass-reactive, armor-piercing shell that contains its own miniature grenade that explodes inside the target after the bullet portion has lodged itself in the enemy. This is the basic Bolt round. Makes your Lasgun look like it was made to toast bread. Even if their armor is pierced they can simply ignore many wounds that would have each killed a normal man. And these are their basic infantry. Mention of things such as the collossal form of the Dreadnought walker, Land Raider battle-tank and Tactical Dreadnought Armor (or Terminator Armor) is enough to make any Guardsman who finds himself facing these foes soiling himself.
A more and more common foe for the Guard to fight is the Tyranid Swarm. Honestly every single Guardsman fighting a Hive Fleet will die, in a very very very terrible way. A bolter shell to the head is mercifully swift compared to these beasts. Not only are they covered in all sorts of claws, teeth, talons, and other ripping horrors, but their weapon symbiotes are just horrific. The Barbed Strangler fires thorned vines that entangle enemys and then slash and strangle them to death. The Flesh Borers fire acidic flesh eating worms that eat through armor and then feast on the victims internal organs. Devourers fire swarms of razor sharp burrowing insects that upon contact simply start burrowing through their prey until they go out the other side. Zoanthropes use their minds to open holes in the warp and create blasts of raw warp energy that vaporizes anything caught in it. Carnifex tear infantry and tanks to shreds like they were paper. And to add to all the fun, there are probably many more Tyranids in the fight than there are Guardsman, so they dont even have the advantage of numbers.
I would go on to talk about the terrible torture of the Dark Eldar, the insanely deadly weapons of the Eldar (whos basic guns shoots monofilament shurikens into you), the overwhelming brutality of the Orks, the sheer invincibility of the Necrons, the ungodly horrors of the Chaos Space Marines (all the fun of Space Marines plus daemons, YAY!) but I think everyone gets the idea.
In summation, if you are ever drafted into the Imperial Guard, just put the pistol to your head and get it over with. I garuntee its probably a much less painful and easier death than your likely to get.
P.S. I didnt mention Tau because quite frankly, even a Guardsman can laugh at tau lol.