I am not writing this out of anger, but more out of annoyance. Lately, it seems like everyone thinks everyone in One Piece has suddenly gotten Haki. They base their theories on one reason or another, and most of them can be argued easily. It seems that they are unable to accept an explanation such as natural power or the character's own strength while slightly tweaking the laws of chemistry and/or physics. I am going to examine some of the most popular characters that are at the center of the Haki conspiracy theories.
Zoro: Everyone thinks he has Haki because of how he cut Mr.1. He said he could feel the power and knew he could cut steel. Let's examine Mr.1 first. all of his blades have been on areas of the body with a lot of bones, like his arms. If you wonder what I mean, hold out your arm so your palm is facing you. Then, starting at the pinky finger, follow the bone line down to the elbow. That is where his blades always appear. He can only turn his skin and bone tissue into the blades. When did an actual blade appear on his stomach? Exactly. Basically, Zoro was cutting through a layer of metal about the same thickness as the skin on your stomach, assuming you are of average male build. He got a confidence boost that allowed him to pull off one last mega-attack. There is not even a suggestion of proof or evidence of Haki.
Nami: Even after Oda explained how Nami could injure Luffy, I still see Haki popping up on her page from time to time. She injures his spirit, it's for comedic effect. On to the next one.
Jinbe: He was somehow able to injure Ace in their fight, it must be Haki. In case anyone forgot, Busoshoku Haki is not the only way to nullify the effects of a Devil Fruit. Sea water also does the trick, and as the Battle of Marineford pointed out, Jinbe has some control over sea water. Also, Ace might not have been able to use his Devil Fruit reflexively by that time. Thus, Jinbe does not have Haki.
Sanji: Diable Jambe. Everyone thinks the only way that could be possible is if it's Busoshoku Haki. It's not, Sanji spins around really fast, subjecting his leg to an immense amount of heat from the friction created, causing it to become heated. It, like most things in One Piece, is a heavily tweaked and exaggerated idea based on real world science. Rub your hands together really fast for a few seconds. What you feel is heat created by friction. Like Dance Powder being based on silver iodide, Diable Jambe is based on heat generated from friction.
Gol D. Roger: This one I actually disagree with less than others.Everyone thinks "the voice of all things" is Mantra (quicker to write than Kenbunshoku Haki). Well, let me tell you, it isn't. Mantra is Mantra, and the voice of all things is the voice of all things. One has to do with sensing someone's location and the other lets him write in Poneglyph. If you think that Roger still had Mantra, then apply it to the real world. By that logic, Joan of Arc had Mantra. However, while it is likely he had Haki, it hasn't been stated yet, and is thus, speculation.
Marshall D. Teach: He was able to injure Ace, he must have Haki, and anyone who punches him must have it too. If you skimmed the explanation of his Devil Fruit even badly, you'd know that he has to let attacks hit him. He can't absorb them like a normal Logia. Think about it, if he absorbed an attack, he would be making a blackhole on his body. Black holes suck in everything around it. That would include the one MAKING the black hole. It's a survival strategy, and sucking someone into his own body just sounds too messy if you ask me. As for his ability to injure Ace, his power lets him nullify the abilities of fruit users. It's a Devil Fruit, not Haki. His Devil Fruit doesn't have Haki either.
Those are the most common ones that I've had to fix on the wiki. If you think you know someone who might have Haki, tell me who, and why you think so, and I can probably disprove it. Also, if you come across one I can't disprove, don't write that that person has Haki on their page, please.