From a purely practical view, this man is correct with the assertion on his t-shirt; it is harder to kidnap fat people. Fat people are harder to pick up and carry away, and therefore it requires more physical effort. We're not sure we'd ever feel the need to wear a shirt pointing it out to other people, but we can't disagree with the scientific accuracy of what he has to say.
Given that he's surrounded by portable toilets, though, we suspect that this man is at a festival, or a similar public gathering. If it's one where people are drinking alcohol, he might have put a target on his back just by wearing this. All it takes is one group of drunk people to look at it and say, 'that sounds like a challenge,' and a few minutes later he'll find himself being bundled into the back of a van and wondering what's going on.