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Tear Jerker: Tin Tin
From the comics
Explorers on the Moon: Wolff, overcome with guilt at betraying the others, leaving the rocket and marooning himself in space in the hope that it will give the others more oxygen; even Captain Haddock, who moments ago thought Wolff had actually tried to commit sabotage, is moved to tears by this.
Tintin in Tibet: The Yeti's grief when Chang leaves.
There's also the Captain trying to sacrifice himself to save Tintin, along with Tintin's reaction to his plan.
Captain Haddock: You can at least save yourself. You must cut the rope, it's the only answer!
Tintin: Never! Either we're both saved, or we die together!
From the animated series
In the scene in "Tintin in Tibet" where Haddock tries to sacrifice himself, he mutters bitterly to himself that he's "just getting rid of dead weight" while trying to cut the rope, which makes the scene all the more painful.
From the film
The look on Haddock's face after Tintin snaps, "I can smell [alcohol] on you!" after Haddock explains that he lost the scroll to the bad guys.
Especially since he hadn't actually been drinking. He was tempted, but the smell came from Allan breaking a bottle over his head.