If their business relies on selling t-shirts that make fun of rape, then I'm with Uppity - I will not weep if they go out of business (though I would feel sorry for the employees who have no influence on editorial policy).
After all - they do have a choice - there are plenty of funny slogans that could be printed on t-shirts, without crossing the line into offensiveness - my reading of the following statement from their website makes it pretty clear that they want to offend and don't care at all:
"We are a bleeding brilliant new website; we will put more information about our bloody business when you buy some rags.
Go buy some rags! We guarantee you will find something you like, and probably dislike.
If you are observant, you may have noticed that Jamrags is an offensive t-shirt company. We specialise in creating offensive t-shirts, cotton for cunts. If you are a cunt, then we'll jam one of these rags in your letter box in exchange for precious metals."
I feel sorry for their girlfriends (if they have any that don't come with their own footpump).