It should be something that means something to you guys as a group like in-jokes or how you all view each other (the cheeky one) or something like that. You could always go down the 'little miss' route but that isnt terribly original! Just all sit down together with a bottle of wine, i'm sure you can come up with something
There has never been a t-shirt with a slogan on that has not made the wearer look like a dickhead. The concepts of not looking like a dickhead and wearing a t-shirt with a slogan are mutually exclusive.