I'm trying to make a shirt too! I really like the last one of yours, Who needs a life? I have Harry Potter.
Some of my ideas and my friends are:
-Make Love, Not Horcruxes
-(On the front:) Edward was a Hufflepuff.
(back:) What a duffer.
-Wrackspurt got you?
-(F:)Voldemort has seven horcruxes?
(B:) I have eight.
-You can do something from your House, like I would do.. LET'S GET ROWDY, RAVENCLAW! Or something like that.
-F: Hey Voldy, I'll put your souls back together.
B: All night long.
-F: HE'S JUST AN ORPHAN WITH A TORN SOUL.
B: Proud member of the Poor Voldy Association.
-SAVE GINNY WEASLEY FROM DEAN THOMAS!
-F: Your mum looks like Voldemort.
B: PWND
It's really fun to think of ones yourself and you can ask friends who are Potter fans, too. Or you can look at Potter-related icons, avatars on iconator.com or bumper stickers on facebook, that's what I did too.
Mine? https://answersrip.com/question/index?qid=20090712161831AA7zBuM