Gatsby notices that the clock is stuck, just like he is stuck in the past. The clock falls and Gatsby catches it symbolizes that he is trying to hold onto the past.
Gatsby's dreamed his entire life of being part of New York's Elite. The elite came from old money and Gatsby was new money, so he could never be a part of the "elite."
Tom calls Gatsby's car a clown car, which offends Gatsby. He calls Gatsby's car this because he is reminding Gatsby that he will always be new money. Tom is also saying that he doesn't need to flash his money because everyone knows Tom is from old money.