Notice how Jerry, in the first 3-4 seasons, having just broke up with Elaine, has a lot more easy-going attitude and is able to come up with wise cracks and intellectual dialogue. Then by the 7th-9th seasons, he really resents people, is obsessed with small, insignificant quirks of the girls he dates, and by the 8th year to the end, he actually resents having people over and prefers privacy and peace. Look how he's aged!

Examples:

S1: "what, you think I go around with this tiny T-shirt scamming dry cleaners out of money?"

S9: [After George or Elaine berates birthdays- it's awful; you have a bunch of people over and you're thinking these are my friends?] ..."Everyday must be my birthday".