Sorry ahead of time for the awkwardness of the pics. I normally do this by holding it in my left hand and using my right hand to fold... so it's hard to do with one hand. The blurry pics are the result of me attempting to click the button with my left hand so I could fold it more naturally :P
My Divacup, size 1.
Step 1: Smush it flat, like the beginning of a C-fold.
Step 2: Pull one side of the rim down toward the stem.
Step 3: Squeeze the corners in, so that the rim is basically closed against itself.
A side view:
Step 4: Pull one side of the rim over the other, to create a sharper point at the top, and hold it in place with your thumb.
The point is very small, and the whole thing is quite flat. It's a little bit wide, but I insert it so the corners are pointing toward the front and back of my body.
The Diamond shape:
A top view of the finished Diamond:
I love this fold. It's pretty quick to accomplish, and very slim and easy to insert. I haven't really had any issues with a delayed pop... if it takes a minute to open, you should be able to just wiggle it a little and it'll be fine. :)
Also, I only have a Divacup, so I don't know how the Diamond will work with any other brand of cup. But if any of you try it out, I'd love to hear how it works!