Olaf's song about wanting to experience the summers he always heard about is pretty much a send-up of a Bubsy-Berkley, Rankin-Bass TV special dance number, with cartoon-ish seagulls as back-up dancers. Cue Olaf in shades, in a hot tub, playing on the beach, dancing around sand people, and relaxing on a picnic! It's also hilarious because Olaf is completely unaware he'll melt in this weather, yet he's so happy and enthusiastic about how much fun he thinks he'll have! When he gets to the line "and I'll be a—", he even skirts around the mention of the word "puddle" when he approaches one, and instead jumps over it and belts out "HAPPEEEEEEEE SNOWMAN!"
"And I'll do whatever snow does... in SUMMEERRRRR!"
"My snow up against the burning sand!"
Anna's and Kristoff's reactions during the song are priceless.
Kristoff: I'm gonna tell him.
Anna:Don't you dare!
And after the song is over...
Kristoff: Somebody's gotta tell him.
Anna and Kristoff are also equally confused randomly showing up in the number sitting at a picnic lunch holding sandwiches. Sven however pays no mind and just eats.
He does, however, say the word "steam," which makes it even funnier.
The gang is sledding back into Arendelle and Kristoff tells Olaf not to expose himself to others. Olaf says he won't and slides behind a house, where this offscreen exchange happens.
"I don't have a skull... Or bones." It's the delivery that makes it.
This line when Winter stops.
Olaf: Hands down, this is the best day of my life... and quite possibly the last.
When he's cooing to Sven after the gang falls down a cliff, Kristoff separates them with an extremely creeped out look.
Kristoff: Don't talk to him that way.
When he finally realizes that he's been calling Kristoff the wrong name all this time.
Olaf's reaction to Kristoff's "family" of trolls, who appear to be rocks. He thinks Kristoff is crazy and tells Anna to make a break for it. Repeatedly, and getting more and more agitated when Anna doesn't run.
Their faces during that scene.
When the trolls shout "Kristoff's home!" and Olaf responds "Kristoff's home! Wait, Kristoff?"
When Anna is telling Kristoff about Elsa's reaction to her engagement, Kristoff is in disbelief that Anna got engaged to a guy she just met and they have this exchange:
Kristoff: Didn't your parents ever warn you about strangers?