11. Hank Discovers Heisenberg - Breaking Bad
No matter how "cool" Walter White's transition into Heisenberg or how clever his manipulation of the criminal underworld to provide for his family, there was always going to be serious collateral damage. It probably cost him his mortal soul and he definitely got Jesse Pinkman into a darker world than he would have himself, but those two pricetags were considerably less painful to watch than what he did to Hank Schrader.
The moment when Hank discovers that Walter is the criminal he's been seeking for years is actually a betrayal free-for-all because it starts when Hank learns that his brother-in-law and most trusted friend is Heisenberg, then Jesse betrays Walt when he discovers that he poisoned Andrea's son Brock and goes to burn down his house. After that, Hank convinced Jesse to turn on Walter, almost betraying him to his ruin and then when Hank is killed by the white supremacist gang, Walter rats out Jesse, tells Hank's killers to kill him too and then tells him that he watched Jane die and did nothing.
It's like a cross-roads of betrayal and it's hard to say which is worst, but Hank's line in 'Blood Money' when he discovers the truth certainly adds weight to his being the most painful:
"It was you. All along, it was YOU! You son of a bitch! ...Heisenberg. HEISENBERG! You lying, two-faced sack of sh*t!"