One of the Ragnarok's best comedic motifs are the repeated callbacks to the first two Avengers movies, as related to Thor, Loki, and Hulk. A lot of them are gut-busting funny, but one or two you may have missed if you're not a hardcore Marvel movie fan.
Here are Thor: Ragnarok's hilarious Avengers callback jokes:
When Thor first encounters Hulk, it's in The Grandmaster's gladiatorial ring. After hearing so much talk about The Grandmaster's savage champion, Thor is thrilled to see that it's Hulk.
When Thor sees Hulk, he signals to Loki (who is watching the match from the Grandmaster's private box) that it's their old friend Hulk. Of course for Loki, the sight of Hulk brings back painful memories -- like, memories of the considerable pain Hulk inflicted on Loki in Avengers. The god of mischief's immediate response to seeing Hulk is to go pale and exclaim, "I need to get off this planet."
Arguably the funniest part of The Avengers is when Loki is delivering an evil declaration to Hulk, trying to assert his superiority as an Asgardian warrior and sorcerer. Hulk's response was to snatch Loki right out of the camera frame and repeatedly slam him, in a moment of cartoonish hilarity.
During Thor and Hulk's bout in the gladiator ring, there's a moment where Thor thinks he's put Hulk down for good. He starts to breathe easy for all of a second, before he too is snatched out of frame, to be repeatedly slammed on the ground.
Best of all is Loki's response, yelling, "Now you know how it feels!" from the spectator booth.
After Thor finds himself imprisoned by The Grandmaster, he begins to hatch a plan to free himself and later Hulk from the Grandmaster's games. Of course that's hard to accomplish when Hulk isn't willing to leave, being perfectly content with his status as the gladiator champion of Sakaar.
When Hulk is first revealed to be the gladiator champion, Thor tries to talk him down, using the same word sequence that Black Widow perfected in Avengers: Age of Ultron. Of course it doesn't work, and Hulk begins kicking Thor's butt all over the ring.
Thor is the persistent sort, though: after Hulk reverts to Bruce Banner, Thor keeps trying his own shoddy version of the "Sun's getting real low" cadence whenever he needs to keep Banner calm.
Thor eventually tries to get off Sakaar by hijacking the Quinjet Hulk arrived on, but he runs into one problem: gaining access to the jet controls. The Quinjet is setup to be voice activated by the various Avengers members, but the keywords were decided on by Tony Stark.
For Thor, this turns into a frustrating and humbling process of guessing what reference Stark would use or him. He starts off with prideful guesses like "strongest Avenger" or "God of Thunder," but after considering the source of the security setup, Thor realizes there can only be one keyword for his access: Point Break.
That's a call back to the moment in The Avengers after Iron Man and Thor have faced each other for the first time. As Stark passed Thor on the Helicarrier deck, he exclaimed, "Nice swing, 'Point Break.'" Tony Stark is never one to let a good joke die.
Loki terrorized Earth in The Avengers by using the Tesseract as a portal through which to launch the Chitauri invasion on Thanos' behalf. After Loki was stopped, the Tesseract was taken and locked up in Odin's vault for safekeeping.
During the climatic battle of Thor: Ragnarok, Thor realizes that Hela can only be stopped by placing The Crown of Surtur on The Eternal Flame, allowing the fire demon to realize his full power and destroy Asgard. Thor battles Hela to keep her distracted while sending Loki to infiltrate Odin's vault.
As Loki is trotting across the camera frame with The Crown of Surtur in hand, he does rapid backtrack back into frame, putting on a wide-eyed expression as he passes the pedestal where The Tesseract is being kept. The Looney Tunes-style sequence is a comedic little callback to Loki's Avengers villainy; we don't see him do anything, but Thor: Ragnarok's post-credits scene suggests that he definitely steals the object again.
Thor: Ragnarok is in theaters now. Other upcoming MCU movies include Black Panther on February 16, 2018, 2017, Avengers: Infinity War on May 4, 2018, Ant-Man and the Wasp on July 6, 2018, Captain Marvel on March 8, 2019, the fourth Avengers movie on May 3, 2019, the sequel to Spider-Man: Homecoming on July 5, 2019, and Guardians of the Galaxy Vol. 3 in 2020.