what you'll need:
1 T shirt
pair of shears
serger (a sewing machine with a step zigzag will also do, but is not shown here)
a tape measure
let's get started
Step 1: Create the pattern
the height of the hat should be more or less fixed. one can see, faintly, a fold line drawn on the pattern here, at about 2 1/4 inch from the bottom line. the lip of the hat will be folded inwards.
you can be creative and add more 'spikes' or make a 'mohawk' hat as well from this basic pattern.
* using the time-worn rule that the cervix has to be 10 cm dilated, using 2.5 cm/inch, and assuming my child was just born (more or less true), we can back out a value of pi to 1 significant digit.