She is known to be Matt Stone and Trey Parker's most hated celebrity. They are quoted as saying, "A lot of our fans ask us 'Do you really hate the celebrities you make fun of in South Park?' And the answer is, of course not. It's all just in good fun... except when it comes to Barbra Streisand. We hate her."
In "Mecha-Streisand", Eric Cartman discovered a strange triangle-like object while on a school field trip. Deciding it was worthless, he tossed it aside, only for Kyle Broflovski to claim ownership of it, at which point it was discovered that the triangle was in truth a rare archeological find called the Triangle of Zinthar. News of the discover goes public, drawing the attention of the musical diva, Barbra Streisand, who realizes it to be the second half to the "The Diamond of Pantheos". The diamond was split into two separate triangles and hidden at different points of the Earth, but Streisand found one of the pieces during the shooting of My Fair Lady. The other piece happens to be the triangle Cartman found, and according to Maltin if Streisand were to get her hands on that triangle she would become the most evil and dangerous creature to ever walk the Earth— Mecha-Streisand.
Streisand rushes to South Park and makes several attempts to get the Triangle from Kyle and later Cartman (who regained ownership of the Triangle). In the end she tourtures the boys with her singing, which horrifies the boys, and causes Cartman to give up his prized possession rather than listen to her tortuous voice much longer. Joining the triangles together, she transforms into Mecha-Streisand and destroy South Park. She is however defeated by Leonard Maltin, Sidney Poitier, and Robert Smith, all of whom take the forms of Japanese movie monsters.
Although she doesn't appear in person again, Streisand remained a constant character of fear and loathing in South Park. In the episode, "Spookyfish", Comedy Central ran an ad campaign during the time leading up to the broadcast of the Halloween episode, stating that it would air in "Spooky Vision" - something so terrifying that it couldn't even be described. As the episode was introduced, it was revealed that this horror was in fact a photo of Barbra Streisand repeated in the four corners of the television frame. Streisand's face was also used for scene transitions in the episode. Each act of the episode featured a different photo.
In the episode, "Osama bin Laden Has Farty Pants", Cartman holds up a series of signs to show that Osama bin Laden is crazy, including "Screw Ball", "Jackass", and an image of Barbra Streisand foreshadowing Parker and Stone's hatred to her.
Streisand appears again as Mecha-Streisand in "200", but with a completely new CGI appearance. After her destruction she was somehow salvaged by Rob Reiner and Tom Cruise, who located and rebuilt the Diamond of Pantheos to revive her, being activated in the episode's climax. In "201" she rampaged though South Park and destroyed a few buildings, killing Pip Pirrip and others. The Super Best Friends tried to fight her but none of their tactics worked, not even removing the triangles. However, Jesus Christ came up with a plan with help from Moses, getting Krishna to morph into Neil Diamond and perform a duet with her where they were able to pacify her. What became of her after this is unknown.
Normally, she looks to be almost deformed, with small eyes, a large, odd-shaped nose, and a double chin. She wears a black sleeveless shirt, a necklace, and blue pants.
In "Mecha-Streisand", It is revealed that Streisand's "mother was a Jackal, and her father was an insurance salesman" and that she is an "evil, egotistical diabolical bitch" who wants to conquer the world with the relic.
- In the episode, "Pre-School", Trent Boyett is upset that he didn't get to have fun adventures like the boys like fighting "a huge mechanized Barbra Streisand".
- In the film, South Park: Bigger, Longer & Uncut, Eric Cartman uses "Barbra Streisand" as an extremely strong swear word to invoke the electricity from his V-Chip to defeat Saddam Hussein.
- A poster for the fictional film, Mecha-Streisand Takes New York appears in South Park: Bigger, Longer & Uncut.
- According to the DVD commentary of "Mecha-Streisand", the main reason why the creators hate her so much is that after Colorado passed the Amendment 2, an amendment to the Colorado state constitution forbidding homosexuals from being recognized as a protected class, Streisand spoke out against the state and all its citizens, calling them a "bunch of hicks" and promising she would never visit Colorado again.
- After her appearance in "Mecha-Streisand", Streisand publicly came out against South Park. She attacked it not for her portrayal as a monster, but for promoting cynicism among children, despite the fact that the show isn't intended for children.
- As Mecha-Streisand, she is based on the monster Mechagodzilla from the Godzilla franchise. In the first episode, she's based on the original version of the monster from the 1974 film Godzilla vs. Mechagodzilla and its immediate sequel Terror of Mechagodzilla in 1975. When she reappears in "200", however, her appearance is based on the third Mechagodzilla, Kiryu, from Godzilla Against Mechagodzilla in 2002 and Godzilla: Tokyo S.O.S., its 2003 sequel.
- Out of all of the celebrities portrayed in South Park, she is the only one the creators truly despise. Their insults were to the point where pictures of her were used in Spookyvision; as well as making her name count as a swear word in certain episodes and their feature film South Park: Bigger, Longer & Uncut. Also in an interview after Streisand came out against South Park, the creators said the fact they were able to get under her skin made them feel awesome.