Its hard to take a picture of yourself wearing that.. but I tried:

//EDIT:
Tutorial: *Sorry the link stopped working!! If you want to see the pictures more clearly, right click>properties, and then copy and paste the URL in a new window
Materials-Hoodie or sweatshirt [duh]
-Sewing machine or needle and thread
-Straight pins
-Scissor
-Felt or other material
If your buying sheets of felt, always get more than you think you need. Its always better to have extra incase you mess up, or underestimated.
*I used a sewing machine for this. You could hand sew it I suppose, but it will take way longer.
First thing you need to do it map out what you want the spikes to look like. I used 3 different sizes, and 5 spikes total.

If you want to do it like I did, I cut out 4 of the first and 2nd spikes, and then 2 of the 3rd one. Make sure to pin the pattern to your fabric when cutting it out.
Make SURE you make the spikes a big bigger than you want them to be for the seem allowance.

The next thing you want to do is sew your spikes together. Its important that if your fabric has 2 sides, to put the two sides you want to be on the outside faced
together when you sew them, so when you turn it right out side again it will work properlly.
The squareish part underneath the triangle is where you put it into the seem of the hood. When you get to stuffing, do NOT stuff it past that "line".
If the diagram below is your spike, then the dotted lines are where your sewing.

Asemble all of your spikes up to that point before you go any farther.
They should look something like this:

The next thing you need to do it turn them right side out, so that they can be stuffed.
Ideally, you should use cotton stuffing for this, but plain old medical cotton balls work as well. Just make sure you pull them apart so it doesn't look all lumpy. Try not to overstuff the spikes either.
Once you have them stuffed, it time to sew up the bottom. Sew it right where the stuffing ends, not at the very bottom edge. Like so:

Here comes the fun part.
Take either your scissor, or a seem ripper if you have one and open the seem that runs through the hood.
I forgot to take a picture beforehand, but once its open, and layed out, heres what it will look like:

Start with the smallest size, and put it almost right at the bottom [sorta above the tag]. Make sure you put it where
when you sew it, only the stuffed part will be seen.
Don't put them RIGHT next to each other, make a little space before putting the next oneon.
Once you pin all them in place, it should look like this:

I didn't do this, but it would be wise to put another pin near the end where there are no spikes, just so its easier when your sewing.
Now your finally ready it sew it back on!!
This should probally be done with a seger, but if you don't have one, or are lazy like I was, you can just was easily use a regular sewing machine. Use a strudier stich than just a single if possiable.
Be very aware of where you put your straight pins! You
have to take them out before you get to sewing that part! Its hell on your machine if you go over pins.
And
TADA! Thats it. If the spikes look messed up, you can always rip them out and try it again.
Here is how your final product should look:

If you make one post it here!