cause their jealous
People call people names because other people think that it is funny. other wise it actually hurts. they call each other names because it makes them feel good from all the stress.
Yes, it still hurts but it just means you guys love each other enough to know it wont do any real damage, and only people that know each other should playfuly call each other names.
Because They have a defense gland located in their brain which allows them to give off signals which we call "Names"
A neighborhood
No, it is unlikely he calls her that. The two of them are very affectionate and caring with each other, and undoubtedly they do have pet names for each other, but they have not made these names public. However, some people have heard them use the word "honey" or "hon" in interviews on a couple of occasions.
Yes but not in front of fanes
That depends, are the vampires and werewolves friends or not? If they are friends, they would probably just call each other by their names. If not, a vampire would call a werewolf a mutt, a stupid dog, and other degrading dog/ behaviour representing names.
a family
People call those under their care, be it a spouse, child or pet a variety of silly things that are usually called "pet names". "Pet" names because we most often do it with pets. It's just a way our species shows affection. You'll notice that whenever we are mad or upset with each other, we always go back to names, including full names!
Big O and Jojo
Because they hate each other (as in Draco and Harry) or that person is their accomplice (as in in the Death Eaters) or maybe they're just British.
Your children and your grandniece first cousins, once removed, but in conversation they would call each other by their first names.