Charlie Dobbs is a employee at the Penalty Box that Jen once had a crush on and eventually dated. He had major appearances in three episodes, all of which dealt with Jen's feelings for him. He was mainly seen in the first and second seasons, with appearances decreasing overall throughout the series (with a peak when he and Jen dated at the start of the second season).
Charlie Dobbs first appearance came in "The Fake Date." There, he garnered employment at the Penalty Box. Jen had a crush on him, and received advice from Caitlin to make herself unavailable, as guys want what they can't have. To further this plan, she asked Jude to pretend to date her. Jude agreed; however, things did not turn out well, as Jude was not exactly the perfect boyfriend. Not only this, but Charlie never acted interested in dating Jen despite her having a boyfriend. At the end of the episode, Jen asked Charlie why he didn't like her only to find out that he had a girlfriend named Jill.
The next major appearance he made was in "Deadbeat Poets Society". There, we learn that he and Jen are now going out. This is the first mention that they are dating. Although the episode focuses on Wyatt, he does play a role in it, as Jen feels guilty that she is in a good relationship while Wyatt isn't in a relationship at all.
"Awake the Wyatt Within" is his largest appearance as a character. In that episode, he is still dating Jen. Unfortunately, Coach Halder has found out, and in accordance with his rules against love at work, whenever he sees them together, he penalizes them by making Jen do push-ups. Why he does this is unexplained, although it can be assumed that he likes Charlie more (an assumption that is later confirmed). Because he always penalizes Jen and never Charlie, Jen gets mad at her boyfriend. This is exacerbated by Charlie not seeing the problem with her having to do the push-ups while he continues to work normally. In order to rationalize her feelings, and in part so she can explain the impending relationship collapse to her friends, Jen then begins to exaggerate his bad characteristics. These characteristics include a vein on his forehead, a slightly-large head, and some of his mannerisms. Eventually, she creates a caricature of him in her head, and eventually angrily breaks up with him.
Since then, Charlie has not been seen or mentioned very often. In "Pillow Talk", he apparently had a bet with Coach Halder over what type of chocolate Jen sat on. In "Another Day at the Office", it was confirmed that Halder prefers him over Jen, as Coach Halder took extra shifts that he promised to Jen away from her and gave them to Charlie, with the explanation that he "like[s] him [Dobbs] better." He also made a cameo in "The Journal." It seems that currently, he and Jen treat each other as fellow employees of the same store.