When a show like Parks and Recreation runs for seven seasons, a lot of conflicts must be established, and all that conflict needs to come multiple sources to keep things fresh. Therefore, Parks and Rec had outright villains like Jeremy Jamm and the Tammys (particularly Tammy 2), who would reprise their roles as antagonists throughout the series' duration.
Additionally, Leslie also would run into speed bumps at her job throughout the show's run. These were mostly caused by people owned by corporate interests (such Kathryn Pinewood or Dennis Feinstein) or those with other nefarious motivations like Councilman Dexhart. But even that's not all, as there were some other characters who may have seemed like friends to the parks department at first, but ended up being foes.
Ron Dunn
In the eyes of Ron Swanson, Ron Dunn was almost a godsend. After Pawnee and Eagleton are forced to merge (in order to save the latter), Ron Swanson comes to face with his Eagleton doppelganger. It's the start of a beautiful friendship, in that Ron Dunn doesn't seem to like to talk much.
Then, Swanson's eyes widen as Dunn begins talking about the importance of astrological signs, frisbee-golf, spirit animals, and the innumerable health benefits of going vegan. Dunn is asked to leave the office by Ronn when he mentions his desire to be a "freegan vegan."
Roscoe Santangelo
As Vice President of tech company Gryzzl, Jorma Taccone's Roscoe held quite a bit of power over Leslie, Ben, and even Pawnee as a whole. There's an argument to be made that his company's data mining puts him squarely in the villain category.
In the real world, this would be true, but Roscoe Santangelo is nothing more than a well-meaning pothead buffoon. Considering he never directly runs against the parks department or operates solely for the desire of financial prosperity, Roscoe's seems to have a decent heart, even if he's gotten in the way of the show's protagonists from time to time.
Officer Dave Sanderson
An early addition to the show, Dave was a character that never quite clicked. As one of Leslie's early romantic conquests (most of whom were done away with rather quickly), Dave could seem clingy. When he made a one-episode reprisal later in the series, he proved this assumption correct.
While Dave does lock Ben Wyatt to a restaurant toilet so he can scurry out to Leslie and profess his love, he's no villain. Still, he's not a hero either. Be it the writing or the presence of Louis C.K., the character is off-putting whenever on the screen.
Councilman Milton
Fielding Milton is a product of his time. It's just that his time was very long ago, and he's still in a position of relative power. No one who wants to de-integrate baseball should have a say in matters of any importance. Milton bumps against Knope when it comes time to vote, but he can usually be talked into just about anything. His coworkers may just have to listen to some sexist and/or racist rambling on the way to achieving progress.
Justin Anderson
Justin Theroux's four-episode stint on Parks and Recreation as Ann Perkins's old friend was a bit of a mixed bag. Justin Anderson, a civil litigation lawyer, is shown to be a friendly man who has traveled the world and has a story for every location, but he isn't as perfect as he initially seems.
As far as Leslie Knope's romantic conquests go, Justin is one of her more fleshed out fellas (pre-Ben Wyatt). Still, the series throws Leslie - and the viewers - a curveball when the curtain is raised on who Justin Anderson truly is. All he cares about is stories, not people, and that includes Leslie.
Jean-Ralphio Saperstein
Jean-Ralphio is an idiot. There are precious few ways of stating it otherwise. However, the man is lovable, even when he's throwing himself blindly through Tom Haverford's career aspirations like a natural disaster. However, since he's a megastar A-lister (in his own delusion of life), he still slides by without a scratch.
Jean-Ralphio is a villain if only because his personality forces him in that direction, because's he's naturally so incredibly selfish. Regardless, viewers often tolerate his obnoxious behavior for the same reason the characters do: out of hope that it might come with the occasional nugget of sage wisdom. However, this sage wisdom may be wrapped up in an inappropriate metaphor about waxing a "b-hole".
Joan Callamezzo
The frequently drunk host of Pawnee Today doesn't have any qualms with standing in Leslie's way. She's not an outright villain, but she is a proud gotcha journalist. And when she's not bursting into a rendition of show tunes in the middle of a white-collar restaurant, Ms. Callamezzo genuinely considers herself a professional - even if others don't see it that way.
Joan Callamezzo is a fun character because she's so reputable in the city of Pawnee despite being utterly inept at her job. From nearly cursing on air to the sight of Lil' Sebastian to passing out on the floor mid-interview with Ron Swanson, Joan is a terrific trainwreck. It's just that sometimes her flames get in the way of Leslie and the parks department.
Jennifer Barkley
Yet another terrific Kathryn Hahn creation, Jennifer Barkley is a character who came back after her initial stretch of episodes to serve as the campaign manager to Paul Rudd's dopey Bobby Newport. Politically savvy to the max, Jennifer Barkley is a brash city woman who likes to win, outgunning Leslie and her campaign manager, Ben Wyatt.
Barkley served as an antagonist primarily during her time with Bobby Newport. But, even then, she would have moments of levity with Leslie and Ben. Be it by lamenting how dirty Pawnee water is with the two or buying them a cappuccino machine for their favorite restaurant, she grows on them and the audience as a whole. Still, when she came back later in the city in more of an ally role, she wouldn't hesitate to scoff in disgust at Leslie and Ben's messy kids, underlining her propensity towards lowkey villainy.
Ingrid De Forest
While the prolific Kristen Bell appeared in only three episodes as Eagleton councilwoman Ingrid de Forest, she made a great impression. Before going on to reteam with co-creator Michael Schur for The Good Place, Kristen Bell brought her trademark chipper zest to what could have been a boring role.
Ingrid de Forest is as rich and snooty as the remainder of Eagleton (a villain all its own), but she's also willing to work with Leslie. And, when Leslie is recalled and subsequently replaced by Ingrid, she seems genuinely remorseful. Ingrid's not an outright villain because she has no direct motivation to harm Leslie, but just being who she is makes her a low-key antagonist.
Chris Traeger
The ever-cheerful and relatable Chris Traeger is one of the series' most beloved protagonists, hands down. Throughout his run on the show, he actually served more as an adversary than anything else, at least when it came to countering Leslie Knope's doggedly persistent agenda.
In season two, he and Ben Wyatt (who is set up as the more abrasive of the two) are auditing the parks department. Season three saw him date then break up with Ann Perkins in such a sweet way that she didn't even understand she'd been dumped. Additionally, Chris's strict by-the-books behavior causes problems. This was never more apparent than in season four when he investigates the relationship between coworkers Leslie and Ben Wyatt. His heart may be in the right place, but he still serves as an adversary from time to time.