The clap is a disease mentioned several times by Knuckles and Cheeto Man. Several characters are implied or stated to have it, including Amy, Rouge, Candy Kong and Jessie. Due to the actions of Knuckles, he, Cheeto Man, and Spyro are also afflicted by the disease.
It is unknown within the universe of Tails Gets Trolled exactly what having the clap entails, though it is implied to be a serious disease as Knuckles uses it to his advantage to ruin Cheeto Man's empire.
- Peach: Claimed to be infected from an unknown source (as Candy Kong suspects) who then passes it on to Donkey Kong. (Chapter 18, Page 3)
- Donkey Kong: Claims to have gotten the clap from his threesome with Rouge and Knuckles (Chapter 11, Page 11), though Candy Kong insists he had originally gotten it from Peach.
- Candy Kong: Infected by Donkey Kong as he mentions in Chapter 11, Page 11, though she claims otherwise in Chapter 18, Page 3. (Note: either way, it is likely that she does have the clap as Knuckles mentions before the party started, he gave the "other girls" the clap).
- Rouge: Infected by Donkey Kong after having a threesome with Knuckles and Donkey Kong. (Chapter 1, Page 12)
- Knuckles: Got it from his three-way with Donkey Kong and Rouge. (Chapter 1, Page 12)
- Patty: Infected by Knuckles, off screen before Cheeto Man's party begins. (Chapter 20, Page 16)
- Jessie: Like Patti, infected by Knuckles before the party starts. (Chapter 20, Page 16)
- Spyro: Had sex with Rogue, who had the clap. (Chapter 18, Page 12)
- Amy: Infected after (knowingly) having sex with Knuckles in order to spare her from becoming one of Cheeto Man’s whores. (Chapter 20, Page 5)
- Cheeto Man: Stated by Knuckles to have the clap from the whores he brings to the party. (Chapter 20, page 11)
- Tonya: Also mentioned by Knuckles to have the clap. (Chapter 20, Page 16)
In summary: Peach contracts the clap from an unknown source. She passes it on to Donkey Kong. Donkey Kong spreads the clap onto Knuckles and Rouge, as well as Candy Kong some time later. Knuckles creates a plan to destroy Cheeto Man and his empire by passing the clap onto him, and passes his clap onto the girls he calls at the party beforehand (barring Rogue and Candy Kong since they already have it), infecting Patti and Jessy. Presumably off-screen, Cheeto Man contracts the clap from one of these girls, and passes it onto Tonya (his "main hoe", according to Knuckles). Spyro unfortunately gets the clap from having sex with Rouge and Jessy. Later in the party, Knuckles willingly has sex with Amy in order to give her the clap so that she can be killed by Cheeto Man and released from her suffering.
Real Life Origins
The clap is a way of referring to gonorrhea, a disease transmitted through sexual activities. It typically results the release of pus from one's eyes or other parts of the body, or swelling.