Let me just say that I hate knitting with cotton. I know all of the properties that make cotton the wonderful fiber that it is, such as it's ability to keep one cool and supa crisp stitch definition, but these very qualities make it an incredibly bad choice for a hat.
The first problem I came across is the blown out ribbing. The more I attempted to maintain even tension, the more it prolapsed into some unmentionable blob of stringy entrails. Whatever. I figured that once I got to the stockinette, all would be gravy. Like any good knitter, I used a jogless join for the stripes. With wool, this would result in beautifully even stitches. On cotton, it makes a really gross ladder of gaping stitches 100x more fugly than a little jog in the stripes.
In the end it came out okay. A hat was made using no animal products and therefore another vegan is kept warm.

Note: Next year he gets a juicer.