Jeff looks like a stereotypical high school jock, and is obviously on some sports team at the high school him and Lisa go to, but it's unknown which one he's on, or if he's on multiple teams.
He loves his girlfriend, Lisa, and cares about her very much, but he also seems to be a stereotypical jealous boyfriend, seeing as how he went over to Dexter's house just to beat up Dexter because Jeff thought that Lisa broke up with him for somebody named Dexter.
While his girlfriend, Lisa, is babysitting Dexter and his sister, Dee Dee, while their Mom and Dad are out on a date, Jeff calls Lisa at Dexter's house and they talk for a little. Dexter, who has a crush on Lisa, comes up with an idea to break up Jeff and Lisa.
Dexter goes to his laboratory and disconnects his phone line, and then he calls Jeff and digitally disguises his voice to sound identical to Lisa, and "breaks up" with Jeff by telling him that she's in love with somebody named Dexter. This upsets Jeff, so he goes over to Dexter's house to see what's going on.
Dexter calls Lisa and digitally disguises his voice to sound identical to Jeff, and "breaks up" with her, greatly upsetting her. After Dexter comforts Lisa and Lisa says that she'd definitely go out with Dexter if he were ten years older, Dexter gets the idea to enhance his age by ten years---but Dexter's teen self isn't nearly as handsome as he initially imagined, as he looks like a stereotypical nerd, and his appearance ends up frightening Lisa.
When tries leaving his house through the front door, Dexter sees someone outside---who turns out to be Jeff. When Jeff asks Dexter if his name is Dexter, and Dexter says yes, Jeff introduces himself and punches Dexter in the face for "stealing" his girlfriend.
- It's unknown how old Jeff and his girlfriend, Lisa, are, but they're presumably around sixteen to eighteen years old, due to Lisa's comment on dating Dexter if he were ten years older.
- It's unknown if Jeff and Lisa got back together after Dexter broke them up.
- Lisa's pet name for Jeff is "Fuzzy Lumpkins," which is the name of a recurring villain on The Powerpuff Girls.
- Jeff is voiced by Jeff Bennett. Both the former and latter share the same first name.