Continuity mistake: Roy closes his comic and throws it onto the desk. The camera flits back to Moss, then back to Roy, and Roy is holding the open comic again and repeats the same actions. (00:06:25)
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)
Continuity mistake: When Denholm is holding the picture of the A-Team, he is holding it on the left side of the frame. When it cuts to him putting it down, he is holding it on the right side of the frame.
Continuity mistake: Near the start when Moss runs and jumps onto the couch, his tie changes positions repeatedly between shots. In close-ups it is up on the couch arm and in all other shots it is under Moss.
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.
Continuity mistake: Near the beginning of the episode, Roy is eating & drinking while the phone is ringing. Eventually he picks it up, then Moss comes in and throws him a muffin. Just before Moss walks in, Roy's coffee cup is on his right on the desk. The next shot, as he catches the muffin, the cup has instantly moved to his left. Afterwards, the cup is back on his right. (00:03:20)
Continuity mistake: When Laura Knightly leans against Roy for the cameraman to take a couple photos, her face is even with Roy's. In the next shot she's above him so her chin is at Roy's eyes.
Continuity mistake: Roy has scratches on his face from his and Moss' 'fight'. In the next scene, the scratches are gone. (00:15:30)
The Haunting Of Bill Crouse - S1-E5
Continuity mistake: When Bill Crouse is in his home, near the end of the episode, he pours himself a glass of whiskey. He looks out of the window and see Jen's 'ghost', then screams and falls to the floor. As he's crawling backwards, he's no longer holding the glass of whiskey - and you don't hear it drop or smash. (00:21:45)
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: 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: 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)
Continuity mistake: Jen's tights change throughout the episode. Sometimes she is wearing black tights, other times she is wearing pale/no tights.
Calamity Jen - S1-E2
Continuity mistake: Near the end of the episode, Roy is helping Jen push her shoes on. While he's pushing one shoe on, you can see Jen has her shoe on her left foot. Two shots later, she is completely barefoot and the shoes are nowhere in sight. After Denholm uses the stress machine on her in her office, she walks out with both her shoes on.
Continuity mistake: When Moss asks if Roy is OK, it shows Moss holding his cup by the handle. In the close-up shot of Moss, his grip is on the cup itself. In the next shot he is holding it by the handle again.
Continuity mistake: During the party down in the basement, after Moss has told the embarrassing Amsterdam story, Roy comes back in the room and realises nobody's laughing. He walks up to Moss and says, "What story did you think I meant?" Roy has a beer in his left hand. The next shot, within seconds, he's shaking Moss by the shoulders with both hands. There was no time frame for him to have put the cup of beer down. (00:22:05)
Continuity mistake: The way Jen's books are stacked changes after she says "pedal stool." The book with the red pages moves to the top.
The Haunting Of Bill Crouse - S1-E5
Continuity mistake: The voicemail Jen leaves for Bill is different than the one Bill listens to. For example, Jen says "stop telling everyone", but when it's played back, we hear her say "stop telling people."
Calamity Jen - S1-E2
Continuity mistake: When the stress management therapist opens the suitcase containing the "stress machine", you can see an electrode on each side of the suitcase. In the next shot, both electrodes have moved to one side.
The Red Door - S1-E4
Continuity mistake: When Moss goes to show Roy the picture on the bottom of his mug, the first shot shows the mug on the desk to Moss's right. However, the next shot shows Moss picking up the mug from a different place on the desk, further to his left. (00:03:50)
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.