Factual error: Adam doesn't want to tell Emmy how he broke his arm, so he says he rode a hoverboard. He says he watched the whole BTTF trilogy, but only part 1 was released in 1985. Part 2 was released in 1989, and Part 3 in 1990.
Uncle Marvin is teaching Barry and the JTP hand signals to use on Wall Street. It is obvious he is making up the gestures, but when he says "Tell her that I'm sorry" he is using an American Sign Language sign for 'bullshit'.