At one point Vladimir is so bored that he suggests to Estragon that they hang themselves, making an offhand comment that it's common for male victims of hanging to achieve an erection before they die. Estragon's response to this is darkly hilarious.
Estragon: Let's hang ourselves right now!
The relationship between Vladimir and Estragon is like an old married couple, moaning and arguing with each other for years yet still sticking together.
Estragon's response when Vladimir asks him how's the carrot he's eating: "It's a carrot."
Estragon finds out that Vladimir's happy despite being separated from him for the night, especially because Vladimir's happy that he didn't have to get up in the middle of the night.
Estragon: You see? You even piss better when I'm not around.
Early in Act 2, Estragon tries to recount to Vladimir what happened yesterday:
Estragon: I suppose we blathered. Vladimir: About what? Estragon: Oh...this and that, I suppose, nothing in particular. [With assurance.] Yes, now I remember, yesterday evening we spent blathering about nothing in particular. That's been going on now for half a century.
The hat-swapping scene in Act 2.
Vladimir and Estragon going round in circles, muttering "Let me see".
Lucky's long, deep-sounding but entirely meaningless rant when he finally starts talking.
Vladimir and Estragon debating whether or not they should help a fallen Pozzo up, while Pozzo screams for help the entire time.
When Vladimir and Estragon believe Pozzo is not his actual name, they try calling him "Cain" and "Abel".
The boy always calls Vladimir "Mr. Albert" for no explained reason.
The Running Gag that whenever someone is close enough to Vladimir or Estragon, they will comment on their awful smell.
Estragon: You stink of garlic! Vladimir: It's for the kidneys.