Thanks for your replies
Actually, I have already found a good website, where I can order a custom-made t-shirts (this is unfortunately a website only in polish language: lubmnie.pl ). They use a very good quality fabric, and they improve/edit your own projects. I want to use the template:
http://www.lubmnie.pl/15-efekt-komiks
This is a comic-effect, so I could take some funny pictures of my boyfriend and put it together in a comic style...
Another idea is just use one funny picture of him saying something like: Trust me, I am a Doctor (and then written in small font a funny explanation of P.h.D) or "Don't make me use my P.H.D voice"
What do you think?

Hello everyone,

My boyfriend is finishing his PhD (in aerospace engineering/composite materials) and I want to create a special gift for him. So I am looking for a funny or inspirational PhD quote which I could place on a T-shirt.
Does anyone know any?