Hot Bloodedness isn't reserved just for people. It can be applied to many things — hair, for example.
Hot-Blooded Sideburns are a pair of short, fiery earlocks typically found on passionate Super Robot pilots and Sentai team leaders that usually offer up a quick visual indicator of their Hot-Blooded character. While they don't have to be huge (though they usually are), they are always spiky and noticeable. Usually, they're paired up with some equally fiery eyebrows for added effect.
It should be noted that "sideburn" is a slight misnomer, as Hotblooded Sideburns are rarely actually attached to the face anywhere below the ears, technically making them sidelocks or, to use the religious term, peyot. They're occasionally referred to as the "Go Nagai Sideburns" (after the famed Super Robot GenreMangaka) to make this distinction.
Due to its inherent association with Super Robot shows of the 70s and 80s, this is also a form of Seventies or '80s Hair, and its appearance on female characters to show how badass they were has nearly died out. Its modern appearance on male characters is often in Homage to these earlier heroes.
Let's just say that there's a reason this trope was originally known as Go Nagai Sideburns.
Pretty much every single Super Robot pilot from the good ol' days. In the 70's, this was mostly because it was a pretty popular hair style, but by the 80's it pretty much became a pre-requisite of being a badass pilot.
The most iconic example has to be Ryoma of Getter Robo (Which, in a bit of irony, was not written by Go Nagai as is widely believed, but Ken Ishikawa. He just pitched the concept, although he was a heavy influence on the art style). Armageddon Ryoma, pictured here, sports a pair so huge that they probably warp space-time.
And the sideburns of Kenichi Go from Voltes V are bigger.
The third pilot of the Nagahama Trilogy, Kazuya Ryuuzaki from Daimos also counts. In fact, a domestic robot comments his hair is absolutely unruly and he only combs it down if he is going to meet a girl.
EVERY SINGLE ONE of the five main Bronze Saints in Saint Seiya. Seiya himself is one of the most iconic hot-blooded characters in anime, and has the bushiest ones. So bushy, they poke from out of his tiara-helmet!
Black Jack from well, Black Jack, has a pairs of these so thick that while Tezuka sometimes forgets to properly draw his hair, body, nose, eyes, and sometimes even his facial scar, he's never forgotten the sideburns.
Jamil Neate, the Amuro/Char/Bright Composite Character from Gundam X, has a rather impressive set of sideburns himself. He's kind of a subversion, as he's more The Stoic than Hot-Blooded. Except when he overcomes his piloting phobia and returns to the battlefield.
Guy Shishioh from The King of Braves: GaoGaiGar sports a pair made of batteries. By pulling on them, he temporarily gains a huge boost in speed and agility, as well as turning gold.
Leiji Matsumoto is a bit fond of this look. Interstella 5555, for example, has these on about half of the main cast. Susumu/Derek of Uchuu Senkan Yamato/Star Blazers doesn't normally have them, but he looks like he does when he puts his helmet on.
An omake of Kekkaishi features prototype designs for the main character, one of which sports a rather magnificent set of Hotblooded Sideburns.
Heinkel Wolfe of Hellsing. Her (or is it his?) partner Yumie's might normally be considered too long to be true Nagaideburns but their sheer fieryness, not to mention her psychotic berserker rageHot Bloodedness, are more than enough to make them count.
A common trait in characters designed by Kazuhiko Shimamoto. You might recognize him as the character designer for G GundamandAnime Tenchou.
Mikuni from Duel Masters. They are so noticeable, the third season dub renamed his character "Johnny Coolburns".
In a villainous example, Full Metal Panic!'s Gates sports a pair of these. He seems to believe they afford him some sort of protection. Just before he dies in the final episode, he fiddles with his hair and muses that maybe he had it trimmed a little too short.
You would think that a story in the firs love genre, specifically Hatsukoi Limited would not have something like this. You'd be wrong, Gengoro Takei, has these as well as the required Hot Blood.
Lordgenome from Tengen Toppa Gurren Lagann, who's so badass his sideburns point sideways. It's probably because he might have been based off of Gendo Ikari, whose sideburns extend all the way to his beard like Lordgenome, and who might or not fit this trope too.
Everyone in the movie and OAV designs of Ranma 1/2. While the manga art gives them only thin lines to separate the ear from the cheek, and Atsuko Nakajima's early anime designs made them slightly more noticeable, her revamped designs for later seasons, movies, and OAVs blew up their sideburns into enormous puffs of hair with intricate detail.
Greece, similarly. He has prominent, fiery earlocks, but he's usually laid-back to the extreme. Unless you're Turkey.
Pretty much everyone in ElfQuest. This might just be the time period (the original series was published 1978-1984), or it might being Wendy Pini being unable to draw the bases of those huge elfy ears; the few characters from the original series that DON'T have these (Skywise, Winnowill) instead have some soft of accessory hiding that particular area.
Elquest's art style (especially Siege at Blue Mountain), owes a lot to The Dagger Of Kamui (which was a manga and then an anime contemporary with Nagai's heyday, though not drawn by him). SABM, also has some of the biggest honking 'burns in series history. Pini must like the look though, her early Law and Chaos Elric work has these on Moonglum (Elric not so much, though she did draw him with a goatee for a few scenes).
And quite fitting, him being largely an expy of Harry Flashman, a fictional Victorian officer, given that Victorian times were the peak of the 'burns popularity. On the other hand, Cain isn't in the least bit hotblooded (at least officially), being in fact a calm, calculating Guile Hero.
Both good guy Katsuya Suou and one of the major villians sport these in Persona 2: Eternal Punishment, and we do see that even in Innocent Sin they both had a pair of these as well.
Raidou Kuzunoha vs. King Abaddon: Raidou Kuzunoha XIV. His sideburns are so ridiculously long and pointy they haven't been able to escape being joked about in fanart, fanfiction, or even their own game.
Kazuma Kaneko seems to have some giant sideburn fetish or something. His character designs for the older Persona games and Digital Devil Saga have some pretty large ones. Including Elly and Ulala... not even the women are spared.
In fact, one possible conversation while recruiting demons has one personality type ask if he could pull off Raidou's awesome sideburns to impress girls.
Xaldin from Kingdom Hearts II has some rather large sideburns. Parodied to hell and back in this legendary fic.
He is easily recognized by his muscular frame, his sharp blue eyes, his braids (don't ever call them dreadlocks; do you know what you have to do to your hair to get dreadlocks?), but most people instead choose to pick him out by his sideburns, which are rumored to think and act independently of him.
Quite a few characters in Sengoku Basara have these, including Yukimura, Keiji, and Toshiie. The real winner is Hideyoshi, though: he has sideburns on top of his sideburns.
Endou from Inazuma Eleven achieves this effect with two long locks of hair, one hanging down each side of his head in front of his ears. Each one curves forward a bit before ending in a spike. They're not exactly sideburns, though, in that they seem to only be attached to his head at around forehead height, since they flap around a lot whenever he moves.
Another example is Rococo, whose locks curve around behind and under his ears, then end in a spike that somehow points up towards his eyes.
Team Fortress 2: The very hot-blooded Soldier has a miscellaneous drop that gives him an epic sideburns-mustache combo that also comes with a pipe.
And now, with the Mutton Mann, the Demoman, Engineer, Medic, and Sniper can get in on the awesome sideburns action.
Papers, Please: When identity supplements come into play, the description field will sometimes say "killer sideburns" (and they are indeed very impressive looking).
Jacques Offenbach, best known for writing the "Infernal Gallop" AKA Can Can music, had a nice pair of muttonchops (and a moustache) after going through a copule of really creepy looking phases. The page also features some other men with nice 'burns.