I've always loved my Irish t-shirts to commemorate my 1/16 Irish heritage. (I know, right? That 'n $5 will get you a latte). I have my old 2005 Old Navy St. Paddy's Day shirt that nice and worn out, as well as some others.
When I was introduced to CafePress.com, I realized I could just do my own if I couldn't find what I wanted. Here's round 1. I love it, and that's the beauty of the site. Do what you like.
Check out what it looks like on shirts here.