Obviously, Urban Outfitters realized that American Apparel (with an assist from pervy photographer Terry Richardson) had dominated the "queasy sexual exploitation" market. They would need to strike out in a new direction of being tasteless. How could they still be offensive, but not so offensive that people who shop at their stores would, you know, stop shopping at their stores? And then, it hit them: make fun of fatties!
And before anyone gets all, "James, America has an OBESITY EPIDEMIC so this shirt is actually just good advice", let me point out that if this shirt was actually meant to be some kind of prescriptive health message to the general public, it should probably say "Eat healthier" or "Get active." Of course, that would be terribly PSA and not cool at all, duh.
(Also, no one wearing this shirt is trying to educate their fellow man about healthy eating habits. That skinny chick is not going to come up to me and say, "James, I really think you should increase your consumption of leafy greens, which are high in iron and vitamin K." You want to educate, wear some pamphlets around your neck.)
Anyway. What is the point, really, of wearing a shirt that is at best a grossly over-simplified and potentially unhealthy message about diet and at worst a barely veiled insult aimed at anyone who looks at you? We’re not in eighth grade anymore, Urban Outfitters! I threw out my bratty Hot Topic message t-shirts years ago. I suggest you do the same.