In English, we say, "Toxicity."

In TES, we say, "Do the right thing. Paarthurnax deserves to die."

Paarthurnax (or “the Old One” according to other dov) is the leader of the Greybeards and the first friendly dragon that the Last Dragonborn comes across in the Main Questline. He assists the Last Dragonborn throughout the game and is also available to help them Meditate on the Words of Power (Fus, Feim, and Yol) which can give some bonus effects to certain Shouts when the Last Dragonborn uses them. 

Biography

During the Merethic Era, Paarthurnax was a lieutenant under Alduin who committed and witnessed many atrocities against “mankind” (specifically Nords) but ultimately defected, and alongside mortals, he betrayed Alduin and taught men how to use the Thu’um. Mankind prevailed and won the Dragon War, with Paarthurnaxx retiring to the Throat of the World to continue battling his lust for power. He also became a follower of the Way of the Voice during this time, a pacifist creed created by Jurgen Windcaller that stated Thu'um should be used for worship rather than the glory of battle. Paarthurnax l became the Greybeard’s grandmaster but would continue to live in isolation at the peak of the mountain. 

During the First Era, Paarthurnax would continue to live in isolation but did make visits to Numinex who was trapped in Dragonsreach.

During the Fourth Era, Paarthurnax would assist the Last Dragonborn in defeating Alduin during the Dragon Crisis, helping them with tasks such as finding and learning the Dragonrend Shout and helping them reach Sovngarde to ultimately defeat Alduin. At one point in the Main Questline, the Blades (Delphine and Esbern) will ask the Last Dragonborn to slay Paarthurnax due to the atrocities committed during the Dragon War that he was complicit in. If the player chooses to not kill him, then he will be present for the Epilogue of the game. He will comment on his desire to teach the Way of the Voice to his brethren and can then be found perched on the Throat of the World’s Word Wall and will continue helping the Last Dragonborn Meditate on Shouts. To continue with the Blade Questline in Skyrim, the Last Dragonborn must kill Paarthurnax. 

Cool Quotes

“Dov wahlaan fah rel. (Dragons were created for domination.) We were made to dominate. The will to power is in our blood. You feel it in yourself, do you not?”

“Dahmaan (Remember) - remember, Alduin also follows his destiny, as he sees it.” 

“Lot krongrah. (Great victory.) You truly have the Voice of a dovah. Alduin’s allies will think twice after this victory.”

“But I cannot celebrate his fall. Zu’u tiiraaz ahst ok mah. (I am sad at his fall.) He was my brother once. This world will never be the same."

Last Dragonborn: I love Paarthurnax.

Delphine, scowling: Love's a strong word.

Last Dragonborn: I have strong opinions.

Last Dragonborn, hugging Paarthurnax: "I can fix them" this! "I can make them worse" that! PATHETIC! I can love them so much that it changes the course of the entire narrative.

Delphine: Alright you! Where are the dragons?

Leara Rose-blade, with Paarthurnax and Odahviing hiding behind the stable: Hi, Delphine. You have nine seconds to tell me why you just broke my door.

Delphine: Why do you turn everything into an argument?

Leara Rose-blade, having just refused to kill Paarthurnax: I'm not arguing! I'm just explaining why I'm right!

Delphine: Paarthurnax is dangerous.

Leara Rose-blade: But you don't have all the facts!

Delphine: Which are?

Leara: I love him.

Paarthurnax, after the Dragonborn declares she'll fight off anyone wanting to kill him: Are you sure that’s a wise decision?

Leara Rose-blade, smiling: I’ve never made a wise decision in my life.

Leara Rose-blade: You’ve always, you know, looked out for me and shared your wisdom.

Paarthurnax: I am pretty wisdomous.

Delphine, after cornering the Dragonborn during Season Unending: So do you have any questions?

Leara Rose-blade: Yeah, I have a lot of questions.

Leara: Number one: how dare you?