JLK2 - while those T-shirts are pretty moronic and tacky, I don't find them sexist or offensive in the same league as the Topman shirts. The only one as far as I can see that is misandristic is the "No Boyfriend, No Problems" one, which is still a lot milder than "Nice Girlfriend, What Breed Is She?" and making light of DV. The offensive ones could be directed at anyone, which doesn't make them good, but as they aren't undermining a specific group's rights I don't find them as serious.
In fact, more of their offensiveness comes from self-deprecation than insulting men, e.g. "Property of My Boyfriend", "Will Fuck For Shoes", "Slut Drop" etc.
However, the ones linked to by spiderpig are blatantly sexist and much more vile for it. I remember seeing girls at school with the merchandise featured there, and never thought it was very funny.