First attempt
This project (see the Rationale for an explanation) is going to be harder than I first thought. Not only do you need to find examples of the least cool thing, but ideally you also need to capture the moment for posterity and Tumblr.
Over lunch with my friend (pictured below with face scrubbed out), I spotted a guy walk in with a t-shirt that I thought clearly qualified for the opening instalment of this Tumblr. It was a very simple "I [heart]" design with the twist that the object of desire was "credit default swaps": a major cause of the financial crash that we're still suffering from. The intention was obviously sarcastic, but there's still an edginess to the literal pro-financial-industry-dodginess message of the t-shirt, which brings it into the least cool thing territory. Would a hipster wear a t-shirt with "I [heart] bankers" for example?
Anyway, I'm new to this photo blogging game, so I didn't want to confront the guy in question (head circled in the photo above) and would have preferred to get a candid snap of the t-shirt. This was too tricky for me, so the closest I came to capturing the moment was as we waited outside the cafe, but again my paparazzi skills were terrible so (as you can see in the photo below) the t-shirt design was blocked by my friend's arm. The best I could do was Photoshop the design in approximately the right place.
Well we're off. Hopefully this goes somewhere.