So is Al; he has spikes all over the place even on the joints. The way his chest bulges out seems impractical but it probably supposed to be an exaggerated sort of sloped armor.
Some armor had the wedge on the breastplate for better deflection.
Luckily for them they don't have to worry much about weight and self-injury, for they are the armor.
In Dai No Daibouken, Dai buys an impossibly cool armor which turns out to be horribly impractical. He ends up throwing half of it away so it fits better.
The armor itself is normal. The problem is that Dai is a Kid Hero who is about a head and a half shorter than regular cast, trying to equip adult-sized armor.
Saint Seiya progressively becomes like this. In the final parts of the series, we see stuff like this◊. Must be noted that even the weakest of the Cloths are powerful magical artifacts.
Naga from Slayers, has spikes on the shoulders of her armour that she ends up injuring herself with every time she raises her arms.
X-Men villain Stryfe wore a suit of armour that looked like it was made out of blades, giving many readers the impression that he'd decapitate himself if he ever shrugged his shoulders.
Partially justified in that Stryfe is a world-class telepath and telekinetic (which is saying something in the Marvel world). His armor is meant to be scary and impractical, because not only does he not need to move to attack his enemies, he doesn't actually need the armor, since wrapping his own telekinesis around his body is more effective. And he is aware of both facts.
Mr. Freeze is often shown in suits of armour that are incredibly large and bulky and look like big badass robots. They do their job keeping him cool. However, the live action version of this suit was 75 lbs, and there is the problem that some are so wide in the shoulder/chest that for the rather average built Freeze to wear them and actually move his arms would have to be cut off and stuffed in the sleeves. In his later appearance in the 90s animated series he adopted a very broad look but it was justified: His body was robotic and his only living flesh was a head in a jar.
The books say that Sauron's physical form during that time was that of a man who had been burned to ashes, but was still alive, and in general was brick shittingly horrifying to look at. This is kind of a subversion, since John Howe went to great lengths to stress the idea that all the armour in the movies must work properly.
This trope was lampshaded by the artists, however, as they joked that Howe specialized in scary-looking outfits with Spikes of Villainy that "could poke your eye out." But he did indeed go to great lengths to actually make it possible to even move your fingers without slicing an artery.
The Green Goblin's armor in the first Spider-Man movie didn't seem to help much when Spider-Man started pounding the living bejesus out of him.
Given Spidey once exploded a telephone booth from the inside, and Norman Osborne has only slightly superhuman strength, he probably would've been reduced to a pulp fairly quickly without the armor.
In Highlander the Kurgan has a skull helmet. He would have been better off with a normal metal one. Possibly justified since nothing but decapitation would do more than annoy him, and the Kurgan is not all that right in the head.
Similarly, in Willow General Kael's helmet has a skull for a faceplate. Half of it breaks off when swatted with a sword.
David Eddings example: Towards the end of The Elenium, Sparhawk and his armor-clad companions enter the abandoned city of a dark god and his insane high-priest. The square outside the temple's main door turns out to be positively COVERED with undead soldiers wearing armor like this, which gives the church-knights pause... until they realize that the undead soldiers are basically brainless, and the armor utterly useless: The Zemoch has never really invented plate-armor, and only saw it during the previous war against the Elenes - who favored heavily-armored cavalry such as the Church Knights. They simply did not understand the idea behind it - all they knew was that it was really scary. So they ended up making armor that looked really scary while being more of a hindrance than anything else...
In The Once and Future King, a character spends at least a paragraph hating on ornate armour, stating that the designs just make it easier for a lance to get a good hold and knock you off your horse.
In The Black Company, The Lady and Croaker have sets of this armor justified that without having magic to protect them, they would be sitting ducks. It looks something like this
It should be noted that they're wearing them to scare their enemies, so it's an invoked trope.
The elves in one of the worlds of The Death Gate Cycle use an ancient armor (now they use magic) to scare dwarves, it's so impractical that an armored elf is unable to get up after he was pushed down.
Mythology and Religion
From the account of David and Goliath: We're not told what Saul's armor looks like, but when he tries to let young David wear it, he finds it to be too heavy and decides to opt for his sling and five small pebbles...
Probably because David at this point was in his mid teens (at most) and Saul was a grown man (and exceptionally tall to boot). Even otherwise practical armor would be cumbersome if it doesn't fit the person trying to wear it.
The Dark Eldar of Warhammer 40000 fame have this kind of armour, with lots and lots of spikes, enough that the warriors should be afraid to touch themselves. Parodied in a Turnsignals on a Land Raider strip here.
Given their proclivities, armour that cuts the wearer up a bit whilst in use is probably approved of.
They put it on by hooking it into their skin.
Chaos Space Marine armour tends to include unnecessary amounts of horns and spikes aswell.
Ork mega-armor and vehicle/walker armor tends to live up to this trope, partly due to deliberately being intimidating and partly because they're pretty terrible at creating anything actually practical.
The First and Forsaken Lion, one of the Deathlords in Exalted, has gigantic soulsteel armor covered in spikes and skulls and anything else intimidating and impractical. It's not like he has much choice to change it out for something more efficient, though, as his Neverborn master basically welded him into it after he screwed up his initial plan for world domination.
Diablo III's barbarian has some body armor with horns that protrude from the body in positions that would be really likely to stab him in the arms.
The Lich King from the World of Warcraft expansion has what looks like Sauron's armor with a few nips and tucks (and skulls. Loads and loads of skulls.), although since neither are human, armor like that is at least justified.
Most of the high level armors count really. They tend to have pauldrons that raise higher then the PC's head (sometimes by almost a whole foot) and make the PC wearing it look twice wider then he is.
And as the character moves in various ways, the shoulders often clip through the body in ways that should result in impromptu decapitation or brain surgery. An egregious example is the night elf female, who due to an unfortunate combat stance when wielding two handed axes, swords, or maces will spend most of the fight with their shoulder spikes embedded in their face.
Intentionally averted by the designers of Half-Life 2. The Combine don't care about intimidation and just wear practical outfits - which makes them significantly scarier.
Their armor is all black and strongly resembles swat team armor, so they probably care a little about being intimidating.
Bear in mind, they're cybernetically enhanced in many ways, so they likely don't need to rely heavily on body armor as much as tactics and efficiency, not to mention invoking fear. Of course... the idea of invoking fear goes out the window near the end.
ADOM has a version that is actually more impractical than scary. Moloch armour weighs a ton and gives huge penalties to speed, dexterity and defense (which is not what heavy armour usually grants anyway) as well as attacks. The only positive quality is that it has an even more enormous bonus to protection. As for scariness, the armour is the (dead) moloch, and they are certainly scary enough, both according to their descriptions and when they lumber towards you to punch you hard enough to shatter stone, or at least to take away a lot of hit points.
Raider armors from Fallout 3 fit this trope to a T. They are made mostly from stuff like old tires, leather and the occasional scrap metal; as such, they provide very little protection but significant intimidation factor. The Pitt DLC adds the Tribal Power Armor◊ which is both scary AND practical. The Broken Steel DLC's Hellfire Armor ups the ante one degree more as it's both scary, practical AND cool.
In fact, the Enclave likes to build badass armors, as evident from this◊ scan.
Another subversion is the Centurion armor from Fallout New Vegas, which, although cobbled together from armors of defeated enemies, is very practical as well as intimidating.
Myth: The Fallen Lords has this with Balor. Not only was his armor spikey, its protective qualities were completely redundant considering how many magical dreams of protection he had woven about himself (which is also the reason most other arch mages in the setting never bother wearing armor.) Balor wore it just for the intimidation factor.
Well, the spikes on his helmet did make for a convenient carrying handle when the Legion lugged his severed head to the Great Devoid.
Prototype hands Alex the Armor power roughly halfway through the story. On the one hand, it reduces damage, looks awesome (and spiky) and means that, rather than having to leap over and dodge obstacles, Alex will plow right through or over them, enemies included. On the other hand, all this comes at the cost of Alex's agility (his main advantage over his foes) and gives him the frustrating habit of smashing objects that could otherwise have been picked up and thrown. His Shield power lacks those disadvantages and will negate all damage when deployed, but has less coverage and will break after a time. And it just doesn't look as cool.
War from Darksiders has armor so ridiculously elaborate, it takes Yahtzee the entire second page of his Extra Punctuation article to describe in detail.
In Command & Conquer many of the Brotherhood of Nods elite units have intimidating armor with helmets and capes, and they all wield some awesome weapons. Yet they provide the same amount of protection as any infantry in the game, and still can't protect them from the harmful effects of tiberium.
Daedric Armor from the later The Elder Scrolls games - noteably Oblivion and Skyrim. It's the strongest armor in the game as well as the heaviest, and gives you a +10 bonus to Intimidation-rolls if you wear a full set - because, well, you look TERRIFYING, all covered with spikes and glowing red bits and chitinous demonic armor forged from demon-hearts and ebony. What isn't adressed in gameplay-terms is that all those glowing red bits should utterly ruin your Stealth-abilities (though the armor's weight will give you a penalty there all by itself), and the spikes should leave you with more holes than a sieve every time you do an Unnecessary Combat Roll. I mean, just LOOK at this thing...
Arguably, Falmer Armor as well. It can be more of less effective, depending on whether it's normal, Hardened or Heavy (the best, but also, well, the heaviest), but it always looks monstrous, and is covered in Spikes of Villainy. In this case, however, it's a Justified Trope - the Falmer makes that armor from the only material they have access to, the Chitin of the Chaurus, which happens to be quite spiky. And the helmet makes you look like a monster because it's the hollowed-out head of a huge bug.
The Fire Nation used to follow this trope, with utterly impractical shoulder spikes. Sokka points this out when a group of water-benders are dressing up in 80-year old Fire Nation armor in an attempt to infiltrate the enemy army.
The armor that Phoenix King Ozai wears in the finale looks very heavy and unwieldly. This is likely why his first move in his battle with Aang is to take it all off.
In one story arc of Darkwing Duck, Gosalyn is transported into a future where Darkwing becomes unquestioned dictator of the world. In order to make her his ultimate successor, he gives her gifts, including a very imposing scary suit of battle armour. The only drawback to it was that she wasn't able to move. But she sure looked impressive.
In fact, many Evil Overlords wear this (even though the list advises against this unless there is a good reason).
Samurai during Japan's feudal era. Part of the design philosophy for samurai armor was to make it look intimidating as well as protective. Some armorers went so far into the "intimidating" aspect that it hindered the "protective" aspect.
In the migi-no-jódan kamae (ward) the sword is held above the head slightly slanted. That in order to avoid the helmet crest of the samurai armour.
Ancient Greeks would sometimes wear pieces of armor made of bones, the idea being to tell your enemy "I killed this animal, and I can kill you, too." Bone would still deflect a glancing blow, making it better than nothing, but it also shattered easily under the impact.
Some people were also making armor with gold. Gold is possibly the worst metal for armor because it is soft and incredibly heavy.
Most ceremonial armor tends to be scary and impractical unless the users have a culture of austerity. This is because the armor is more intended to impress the commissioner and display the skill of the craftsman than to protect the wearer.
Bronze armour. Invented in the 3rd millennium BC. Useful against stone, wooden and bronze weapons, immediately obsoleted by invention of iron and beginning of the Iron Age. Still clung to the end of the Classical era. Goliath's armour in the Bible was most likely a bronze lamellar (klibanion) armour.