A giant insult in Anglo-Saxon England would have been to call someone a "nithing". This word essentially means "vile coward" "villain" or "waste of space". It was often a title given to criminals, murdering scum, oath-breakers, those without honor and other lows of society. In ancient Germanic mythology, a nithing was a mythological creature. This creature was supposedly a fiend that caused harm and undoing to other people, often through magick. One solution to this problem was to scold the nithing. Which literally meant screaming at them (which I advocate in ANY situation) until either the spell broke/ or the person revealed their true nature. (Of course there was retribution if someone was accused of being a nithing, was screamed at, and later found to be innocent). There are historically some rune-stones that while dedicated to describing honorable feats of men/women, do save some space to condemn certain nithings.
So what is a nidstang you ask? Well let me have the pleasure of telling you. :) Nidstang means "cursing pole", quite literally. Sometimes it is just called "Nithing" which is why I gave you the back-story to the word. The purpose of a Nidstang is to formally curse or hex someone whom you think really deserves it. The pole can also be used as a sort of protection. You make the pole, leaving the name blank, and place it in front of your home facing the road or something similar. This sort of "curses" unwelcomed or unwanted guests and visitors.
The pole is made like this: A large pole is made out of some form of wood. The wood is not important, unless you are specifically looking for something that has meaning to you or the person you are cursing in particular. You sharpen the ends of this pole until they are nice and pointy. Then, you inscribe certain things into the wood: the name of the person you dedicate this pole to, the actions they have done against you, what you wish to happen to them. You would add binding or cursing runes, runes you found suitable, etc. You may write the person's name repeatedly. You then speak the things you have written. This is called "nid", or the verbal cursing. You may choose to use specific deities in this: a common one is Hel, Goddess of Death. But any and all can be called for this purpose.
Here's an example from the Saga of Egil Skallagrimsson:
"Here I place this "nidstang" ("curse-pole"), and turneth it against King Eirik and Queen Gunnhild - turneth I this against all the gnomes and little people of the land, that they may all be lost, not finding their homes, until they drive King Eirik and Queen Gunnhild out of the country."
After the Nid is done, a horse's head is cut off and place on top of the pole (though sometimes they would use the entire carcass or skin, or if they weren't as serious about the curse or just didn't want the mess of a horse head, they would carve one out of wood as well or use a skull) and the pole is then turned in the direction that the user wishes to send the curse. Ideally, this would be in the direction of the individual's home you wish to curse, the country you wish to curse, the people you wish to curse, etc.
More common today is a "virtual nid": usually someone will type up a nid and send it attached with a picture of a horse's head. I do not think these are effective at all. Perhaps the Nid would be, in calling the Gods or wights or whatnot to take retribution on someone for you. But without the physical presence of the pole- I cannot say.
The size of the pole depends upon the person, really, and the purpose for the pole. You can make a giant one, if you feel you are cursing many people or you want it to be extremely powerful. However, for individuals you can make some as small as wands, etc. I've heard it suggested that if you carve the horse head instead of using a real one, it is best to smear your own blood upon it to "wake" it. Some smear the blood on the teeth of the horse.
You do also have to be very careful and specific with this. It is possible that you curse more than you intended. It can curse the land around the individual you meant to curse as well, and this would technically be driving away the land wights. This is because the idea of the pole is to anger the spirits near the person and cause them to take their anger out upon the intended victim. Sometimes the intended purpose IS to drive out the wights, and this is called "alfreka" or "driving away the elves": this is to make a land spiritually dead through your cursing. This is not something to be taken lightly or done in jest! You need to be knowledgeable in what you are doing, or it could go badly for you.
From my own personal uses and experience with this, I have used a variety of different things to substitute for the horses head when I could not get one. I've used goats head, deer head, dog head, etc. I do not use them UNLESS I am VERY serious about what I intend and have thought it through. Yes, they can backfire on the person using them. Yes, I take the mentioning of it very seriously. No, it is not to be used for petty offenses or grudges. In my entire life and years of practice, I have raised 5 nidstangs and 2 of them were for the same person.