I thought I was original... Me too, but I just work on designing custom t-shirts, like this one https://teespring.com/electronics-dont-love-you-back?pr=SERB or this one https://teespring.com/270-percent?pr=SERB , I guess it is not as interesting as making your own.

You can actually make and sell shirt designs about coding, like this one I created https://teespring.com/electronics-dont-love-you-back?pr=SERB or this one I also created https://teespring.com/270-percent?pr=SERB the links are with big discounts. This site enables maximum 10$ profit per sold shirt which costs 20$. Of course then you need to somehow get people to see them to buy them, but if you have some websites I guess you will not have this problem. So the sites are https://teespring.com for selling entire shirt designs and https://www.spreadshirt.co.uk for selling only the image for the shirt, at around 5$.