If you've ever walked across a college campus in the rain, you know that wellies are a higher education necessity. That's probably why my mind ties them to lazy collegiate outfits. I feel kind of weird wearing them now, like I should be more adult or something.
Making them intentionally part of a look, though, could turn that around. To do that, I'd trade out blue jeans and a knapsack for something either ridiculously fun, like a bright, sparkly dress, or New England summer camp-y, like tattered khaki shorts.