Buzz earnestly explains to Woody his role in saving Earth, basically as R2-D2 in A New Hope. His voice and the music build dramatically, then:
Buzz: And you, my friend, are responsible for delaying my rendezvous with Star Command! (beat) Woody: You! Are! A! TOOOOOOOY! You're not the real Buzz Lightyear, you... you're an action figure! You are a child's plaything! (beat) Buzz: You are a sad, strange little man. And you have my pity. Farewell. Woody: Oh yeah? Well, good riddance, ya looney!
Made even funnier by Woody maintaining a "WTF" look throughout Buzz's story until he finally snaps.
When Toy Story 3 was knocked off of its 100 rotten tomatoes review level by two contrinarians who gave bad reviews because they wanted to be contrary, the director responded by tweeting "You are sad, strange little men, and you have my pity."
Then there's the squeaky noise Buzz's head makes...
Buzz, looking all calm, says Woody's right and walks off to get it together.
"Oh, I'm a sham! Look at me, I can't even fly out of a window! But the hat looked good? Tell me the hat looked good. The apron was a bit much... Years of academy training, wasted!"
Though it's also a bit sad since it shows how awful his Heroic BSOD is, it's hard not to start laughing when Woody turns to look for Buzz and finds him swinging his own arm through the air making airplane noises, then crashing it into the ground.
Ditto for Hamm. "Oh for crying out loud, they're all in boxes, you idiot!"
Mr. Potato Head and Hamm play Battleship, especially when you notice Potato has called every spot on Hamm's grid except the ones where his ships are.
And Hamm has done exactly the opposite, having not missed once. Considering that out of the 100 squares on a typical Battleship grid, 17 of them will be occupied by ships and 83 aren't, it's anyone's guess how they managed that.
Woody miming friendship with Buzz's arm.
And before that:
Woody: Buzz, could you give me a hand?
Buzz: (Throws his arm at Woody)
Woody: Aha...that's very funny, Buzz THISISSERIOUS!
"I don't believe that man's ever been to medical school."
Buzz explains to Woody that revenge is something that isn't encouraged on his planet... then clarifies that they're not on his planet to which Woody responds with an Oh Crap face and saying Little "No".
And it's right after Woody was happy to see Buzz is alright and is confident that Buzz will tell the other toys it was a freak accident.
When the toys are finding out what Andy got for his birthday.
Green Army Soldier: Okay, it's bedsheets.
Mr. Potato Head: Who invited THAT kid?
Sid sleep-talking: "I wanna ride the pony."
Woody tries to get Buzz to follow him back to Andy's by convincing him that he's found a "spaceship" to take him home:
Woody: It's a special spaceship! I just saw it! Buzz (excited): You mean it has hyperdrive? Woody: Hyperactive hyperdrive! And astro...uh...turf!