Sam in that green plaid and Dean in a red shirt; the daily double of awesome shirts
Dean wandering around the store
Sam telling him not to touch anything until they figured out if it was trying to kill them
Nazis. I hate these guys.
Hipster douche and his stupid beard burned to a crisp
Hey, that's not nice; all he did was try to score with Hitler's great great grandniece
Sam's embarrassed little wave at the waitress in the diner
Dean pointing his gun at Kristoph
The scene with the Winchesters and Ellie and Kristoph in the office, with Dean being all casually threatening and Sam being protective
Sam talking about being Lucifer's intended vessel
The fight scene in the office
Kristoph fighting back against his Nazi father
The diner scene, with Sam being all casually annoyed and Dean pointing his gun at Kristoph under the table and 'career day at school was a nightmare'
Sam smacking Kristoph in the head, in particular
The grenade launcher
Sam and Dean realizing this guy is actually Hitler now
Hitler being all hip and goofy
'I killed Hitler'
Something else which I will discuss in the comments