Dawnguard VS. Player Vampire: With Vampirism, the dawnguard will be hostile.

Frostmoon Invitation: A hunter will direct you to Frostmoon Crag. You will have business there. Approach a hunter.

Report to a guard if you notice a crime.
Bitten by a vampire: If you have a potion of Cure Disease and approach a hunter with Sanguinare Vampiris, hand the potion over to the hunter.
Dark Brotherhood Assassin Sent to Kill Player: You must be level 5 for this to happen. If you are attacked by an assassin, report to a guard. If you are a member of the Dark Brotherhood, the assassins will like you.
Dwemer Junk Peddlers: Two children sell dwemer junk to a merchant. Have the children apologize to the guards for selling dwemer junk.
Farmer Leading Painted Cow to Giant Camp: You will randomly encounter this farmer and a cow with drawings on it. Kill the farmer or report to the guard.
Adventurer on the way to nearby dungeon: Tell them the name of the nearest dungeon, or arrest them if they are not nice.
Bandit Killed with Horse Left Behind: You can see a bandit by a broken wagon, but it is dead. Examine the body.
Human changing into werewolf: If you encounter a hunter in werewolf form and you're in human form, run away from it. If you're in werewolf form, aid it.
Werewolves: This can cause the werewolves to attack you if you are in human form. If you're in werewolf form, they will not grow suspicious.
Werewolves VS Vampires: If vampires approach werewolves, it will be a duel against the werewolves and vampires.
Werewolf Kills Loved One: If a hunter kills his wife while in werewolf form, transform or report to a guard of the hold with the incident.
Wolves Hunting Deer: If you like to hunt wolves, kill the wolves. If you're in werewolf form, protect the wolves.
Thief Lock Picking: If you wear Nightingale or Thieve's Guild armor, help the thief. If not, report the crime.
Death Hounds: A death hound can be found at night with a vampire. Kill both the death hound (The dog) and the vampire.
Thalmor VS. Player: Three members of Aldmeri Forces want to execute you.

These are for hunters.
Human changing into werewolf: They will be hostile in werewolf form unless you are in the same form as them.
Hey you there, take this: After that, a hunter will ask about the fugitive.
Hunter and Dog in the Wilderness: You see a hunter that owns a dog, but the hunter and dog might both be strong together.
Hunters Chasing: Hunters always hunt wildlife. They hunt goats, cows, beasts (Including Lycanthropes), deer and elk.
Frostmoon Invitation: If you're a werewolf in human form, a hunter will direct you to Frostmoon Crag.

If you don't listen, these can happen.
Bounty Hunters VS. Player: They will execute you because you're a master criminal.
Just Throw Trash: This will happen if you litter. You cannot do that in werewolf form. Littering is illegal and against the law.
Drop Weapon, Guard Extorts: Guards do not want you to leave weapons lying on the ground. If you say "Don't Care," they will threaten you with jail. Refusing the bribe is a bounty of 10 gold, but you only have to go to jail.
Transforming in a guard's sight: Transforming into a werewolf in a guard's sight will cause the guard to say "Kill the beast!" but it's a handy way to get the Master Criminal Achievement.
Extremely High Bounty: If you commit enough crimes, you might face the ultimate punishment; Death.
Killing Livestock: The livestock owners will report to the guards, causing the guards to arrest you.
Approaching a guard while in werewolf form: While you're in werewolf form, nearby guards will attack you. It can be easy if you're with others in werewolf form. The world interaction also happens after drinking from the Underforge fountain.
Death of Hunter: Whenever you are noticed in werewolf form by a hunter who is not in the same form as you will try to attack you. This does not require approaching a hunter in werewolf form while you are in the same form as that hunter.
Biting someone as a werewolf: That can infect someone with Lycanthropy, and the one who was bitten might be transformed and will aid you.
Arrested close to a corpse: If you tell the guard "Doesn't scare me," they will arrest you with a random amount of bounty.
Rampage: When you wake up outside the underforge and become a werewolf, no members of the companions will be hostile to you, but the guards will. This interaction ends after blacking out a second time.
Talking to Aldis with a Stormcloak Vest on: Not apologizing is a bounty of 40 gold. Then the guards will attack you, then they will arrest you. Your only option is to go to jail for a couple days.
Invading a town: Attacking the guards will cause them to attack YOU.

This does not occur a bounty.
"Can I have that armor:" Dropping any clothes or armor will let you have to answer their question.
Child scares NPCs: Making a child invisible causes him/her to surprise an adult. Then you must laugh.
Bard At Rest: A bard can be found wandering on the road.
Bard Traveling on The Road: Talsgar, a bard can play any song. Place Riften guards by Talsgar. You can pay him a song.
Killing a werewolf: Don't do that while in werewolf form. If you have Dawnguard, werewolves can be encountered on the road at nighttime. It is hard to kill werewolves alone. (Evenly Arsel Pinder from ESO)
Keeping a town safe: You can assist the guards if a settlement is under attack by enemies. Don't attack the guards. You must be in human form to do that.
Courier Delivering an Important Message: Don't forget the message. (Thats a WoW interaction, too)
Headless Horseman: A ghost horseman without a head rides a ghost horse. If you have a horse, ride with the headless horseman. (There's a screenshot of Neytiri Tendaril doing that)
Netch Hunting Party (DB): Encountering hunters on Solstheim is okay. They like to hunt netch for their meat.
Dragon Fly By: You, the citizens and the guards can see a dragon flying over the settlement you're in. The dragon will not attack you unless you attack it.
Dawnguard Vampire Hunting: If you are not a vampire and you are a member of the Dawnguard, help it and their huskies hunt down vampires. (Vampires are considered undead)
Attacking Vampires: Being a non-vampire allows you to attack vampires and their death hounds. They will be passive if you're also a vampire.
Taunting Adventurer: Report to a guard. Taunting the adventurer back makes it attack you. Do not be a criminal like the adventurer.
Dawnguard Novice Hakar: If you are not a vampire, aid Hakar. If you are a vampire, aid the vampires.
Dragon VS Giant: This can usually happen while you're in werewolf form. You must complete The Silver Hand & Dragon Rising.
Dragon VS Player: It's much more likely for you to fight the dragon with guards. Doing that in werewolf form is illegal.
Atronach mis-summoned: The summoned atronach attacks the witch it was summoned by.
Attacking five wolves at once: This does not require you to be in werewolf form. A werewolf might cause you to flee and make the wolves come to the aid of the werewolf.
Leaving a werewolf behind: If you're a werewolf in human form, leaving a hunter in werewolf form in a cell and using the lock cheat will prevent the werewolf from attacking you. (Also appeared in Daggerfall)

Starting a Hunt: At 10:00 each night when you have Lycanthropy, transform (Unless you are being seen by a guard).
Aiding the wolves: Wolves will be passive while you're in werewolf form. Causing people to run away makes nearby wolves come to your aid.
Hunters in werewolf form: They will come to your aid.
Aela the Huntress: She will also be passive when she helps you.
Being a Vargr: If your level is at least 48, you can be considered a Werewolf Vargr. It is nonsense to attack a wolf cousin.
Encountering more werewolves: They will deal more damage to guards.
Followers in Service can transform: This was a parody of the screenshot Neytiri Tendaril (Left) and Lydia (Right) [werewolf forms]
Feeding on Blood: Whenever you have Dawnguard, doing that enough will give you the message "Werewolf Perk Available" and you can upgrade the werewolf skill.
Other: Howling at Masser or Secunda is a werewolf power.

Showdown Inferno: You have to cause an inferno to a dragon. This was one of the screenshots of Neytiri Tendaril.
Lycanthropy: You cannot catch diseases, but you can transform into a werewolf.
Being bitten by a beast or vampire: Being bitten by a vampire progresses to vampirism. Being bitten by a werewolf progresses to Lycanthropy.
Being a vampire: This makes other vampires passive and the Dawnguard hostile. The Dawnguard can find and attack you if you have Sanguinare Vampiris.

That's all interactions.