I don't see anything offensive about this. Now, the zombie recreation of The Last Supper where they're eating the body of Christ? That's pretty offensive. This is an homage, an innocent parody that injures none and doesn't portray Christianity or Christ in a negative way. It's just some cats, ya'll.
For the record, I was raised Catholic, abstained from religion for several years and am now a practicing Buddhist. For those that asked "if this was Muhammad..." I have a question for you: if this t-shirt had a fat cat in a robe, sitting in the lotus pose, would you be so riled up about my religion being mocked? Buddhism is the 4th largest religion in the world, but our symbolism and imagery are used and parodied constantly. The difference is... most of us couldn't care less. I have never met a fellow Buddhist offended by the Hello Kitty Buddha, the thousands of nonpracticing people who have Ohm tattooed on their back or the dozens of other bastardizations of our religion.
This shirt design is a parody of one of the most famous paintings in the world. There are many parodies of this painting, along with the Cistine Chapel paintings and tons of other Christian relics. These images are part of our culture as a whole, not just your religion, and are thus subject to critique and parody - like any other widely referenced or recognized imagery in our culture.
TL;DR: get over it, your religion is not special and you need to take yourselves a little less seriously.