Community Season 1 Episode 13 (01/14/10)
This episode was based around guest star Jack Black and Jeff's attempts to change.
The show was clearly winking at critics in its 2010 debut, as Joel McHale's first lines addressed the criticism that his character is too much of a bitter jerk. For most of the episode, therefore, Jeff tried to be laid back and just crack wise.
It sort of worked for him, as Jeff initially didn't seem to mind the fact that some dude named Buddy (Black) from Spanish class simply infiltrated the study group and wanted to join. The guy was sort of obnoxious - it is Jack Black, after all - but it led to some funny exchanges between group members, as they decided whether or not to expand, haze new people, etc.
Jeff was also placed in charge of the Greendale newspaper, a job he relished because it gave him a nice office and the chance to boss people around. But he had to get serious with Annie when she wanted to expose the dean's racist text messages (don't ask) and the dean went to Jeff to help. Turns out, people need him to lead, not lie back and just throw out occasional one-liners.
Abed helped to inspire this in Jeff by constantly comparing him to MASH character Hawkeye, a reference few viewers likely understand.
By the end, Jeff took control and physically dragged Buddy away from the group. He then re-considered and gave a nice speech about how jealous he'd be to see all these "cool" people studying together, so how can he blame Buddy for wanting to be a part of that. Just as the group let Buddy back in, they - and viewers - were in for a surprise:
Another study group, led by Owen Wilson, had taken a vote and chosen to take on Buddy as a member. He was psyched and bid farewell to Jeff and company as the episode ended.