"A" was an iconic part of Pretty Little Liars. As a villain that constantly proved to know everything about the girls, it was nearly impossible to keep anything from "A." Although they occasionally managed it, "A" was often several steps ahead. "A's" actions were always considered problematic regarding the invasion of privacy and actively harmful things "A" had done, including manipulation and nearly killing the girls on numerous occasions. While some fun of the show was questioning how far "A" was willing to take the game, there were times when "A" took things too far.
The three "A's" on Pretty Little Liars had a vastly different way of going about things. Although each of their actions somehow resulted in Aria, Spencer, Emily, and Hanna being in trouble, Mona, Charlotte, and Alex were all willing to achieve that goal through different means. Mona's "A" was terrifying. As the first of the villains, "A" always knew about what they were doing and how to force them into situations that would make them uncomfortable. Charlotte changed things up, going for a more violent approach between body parts, bones, and kidnappings. As the last "A," Alex made some dangerous calls of her own.
6 Dental Work On Hanna
What was initially meant to be Hanna sleuthing through the dentist's office for clues about Alison and Bethany resulted in a far more violent afternoon. "A" had shown up at Hanna's visit, proving how close "A" could get to the girls. When Hanna meets up with Spencer, Emily, and Aria, she is in pain from whatever "A" had done after knocking Hanna unconscious. They find a note caught in Hanna's mouth, left for the group by "A." Although "A" had done other things, such as leaving them alone with dangerous animals that nearly killed them, doing dental work on Hanna, and directly affecting her body, it was a step too far.
5 Toby's Fake Death
If Toby being on the "A-Team" was not bad enough, Spencer was in for a horrible shock when she found his body in the woods. Although a helmet covers his head, Toby's tattoo is visible, and Spencer is horrified to discover Toby is dead. Toby's death results in Spencer spiraling and ending up as a patient in Radley Sanitarium. Although Spencer later learns that Toby was alive, Spencer had taken on a massive emotional hit by taking on the horrors of him being on the "A-Team" and having died.
4 Torturing Hanna
Charlotte's death brings about a brand new "A," calling themselves "A.D." The new "A" has one goal: to know who killed Charlotte. To do that, "A.D." terrorizes the girls. When she does not get answers, "A.D." pushes the limits, capturing Hanna and torturing her while telling Hanna's friends that if they do not reveal Charlotte's killer, Hanna will die. While "A.D." has Hanna captured, Hanna is severely injured, and terrified, desperately wanting a way out. "A.D.'s" torture leaves Hanna with more PTSD and scars from the experience.
3 Impersonating Spencer
The big plot twist in the series finale of Pretty Little Liars is that Spencer Hastings had a secret identical twin, Alex Drake, that no one knew about. Taking advantage of being identical to Spencer, Alex impersonates her, tricking everyone at various times. However, there is one instance in particular where Alex's impersonation is too out of line. When Toby is visited by who he believes is Spencer, the two sleep together. Toby is not aware Alex is sexually assaulting him, but she is more than aware that Toby believes she is Spencer. Toby had been sexually assaulted before by Jenna, so having him experience sexual assault again is having "A.D." go too far in her Spencer impersonation.
2 Causing Alison's Pregnancy
Messing with the girls' bodies should never have happened, but this one makes Hanna's dentist appointment seem like child's play. "A.D." takes advantage of Emily donating her eggs for a messy purpose. When Alison realizes she is pregnant, she initially believes it is her and Archer's child. However, that is not the case. "A.D." had gotten involved, mixing Emily's eggs with Wren's sperm and inserting them into Alison's body. Alison and Emily eventually go on to raise the children together, and it is not until the series finale that anyone finds out who the biological father is. Still, forcing Alison to become pregnant was crossing a line that never should have happened.
1 The Dollhouse
Perhaps the best example of group torture in Pretty Little Liars is "A's" long-con to get Mona, Spencer, Hanna, Emily, and Aria in the Dollhouse bunker. Although Mona had faked her death earlier in the season, Mona's death had triggered Alison's arrest as being responsible for killing Mona. That led to Hanna being named Alison's accomplice, as well as Emily, Aria, and Spencer. So the long-con gets Hanna, Emily, Spencer, and Aria to be taken to a separate facility than Alison as a way for "A" to hijack the van and bring the girls to the Dollhouse.
While trapped in the Dollhouse, each of the girls wakes up in an identical copy of their bedrooms at home, must throw a fake Prom, and are tortured by different games, asking each of them to be willing to risk the other's safety. "A" also puts tracking chips into their necks after knocking them unconscious.