Fifty-Fifty - S1-E3
Continuity mistake: When Roy and Moss are in the basement talking about the night before, just before Jen comes in and we hear her laughing, Roy has the wooden stick from his coffee hanging out of the corner of his mouth. In the next instant shot showing the side of his face, as Jen walks through the door, it has gone. (00:03:30)
Fifty-Fifty - S1-E3
Continuity mistake: The security guard (the guy Jen fancies) is sitting on the couch reading a big thick book. The first two shots show him holding the book from underneath, a few pages in. The next shot, his hands have changed position and he has instantly read through to almost the end of the book. (00:07:05)
Fifty-Fifty - S1-E3
Continuity mistake: When Roy and Jen are arguing about women wanting bad guys, there is a white mug in front of Roy on the desk. In the next shot, another cup has appeared behind it. (00:08:50)
Fifty-Fifty - S1-E3
Continuity mistake: Jen is sitting at the sofa with the phone on her lap, waiting for Daniel's call. She is wearing no shoes. In the next shot, she stands up and instantly has black high heels on. (00:14:30)
Fifty-Fifty - S1-E3
Continuity mistake: In the first few shots, the mess on Roy's forehead is quite a long smear. When he steps out of the taxi, it is now a small blob.
Answer: The shirt is available from www.ThinkGeek.com and is fairly popular in the nerd culture, so it's possible you've seen it in real life or online.