Flanders: I guess we'll just have to agree to disagree.
Skinner: I don't agree with that.
Homer: How could you? Haven't you learned anything from that guy who gives those sermons at church, Captain Whatshisname? We live in a society of laws. Why do you think I took you to all those Police Academy movies? For fun? Well, I didn't hear anybody laughing, did you? Except at that guy who made sound effects. [Makes sound effects and laughs.] Where was I? Oh yeah. Stay out of my booze.
Day of the Jackanapes - S12-E13
Sideshow Bob: Urgh. Rakes, my arch-enemy.
Bart: I thought I was your arch-enemy.
Sideshow Bob: I have a life outside of you, Bart.
Mrs. Krabappel: Now I don't want you to worry, class. These tests will have no effect on your grades. They merely determine your future social status and financial success. [She looks at Bart.] If any.
There's No Disgrace Like Home - S1-E4
Homer: Sometimes I think we're the worst family in town.
Marge: Well maybe we should move to a larger community.
$pringfield (or How I Learned to Stop Worrying and Love Legalized Gambling) - S5-E10
Bum: Got any spare change, man?
Grampa: Yes! And you ain't gettin' it! Everybody wants something for nothing. [He walks into the Social Security Office.] I'm old! Gimme gimme gimme!
The Two Mrs. Nahasapeemapetilons - S9-E7
Apu: Okay, quickly, what is your favourite food, book and movie?
Manjula: The answer to all three is 'Fried Green Tomatoes'.
And Maggie Makes Three - S6-E13
[Maggie is being born.]
Homer: Aw, it's a boy! And WHAT a boy!
Dr Hibbert: That's its umbilical cord. It's a girl.
Tree House of Horror VI - S7-E6
Homer: Please, don't eat me! I have a wife and kids! Eat them!
Tree House of Horror IV: The Simpson's Halloween Special IV - S5-E5
[Homer runs naked through the kitchen, where Patty and Selma are eating.]
Patty: [after seeing Homer.] There goes the last lingering thread of my heterosexuality.
Homer: Kids, you tried your best and you failed miserably. The lesson is, never try.
Blood Feud - S2-E22
[Homer goes to the post office to get a letter he accidentally sent to Mr Burns.]
Homer: [In an obviously fake voice.] Hello, my name is Mr Burns. I believe you have a letter for me.
Post Office Clerk: OK, Mr Burns, what's your first name?
Homer: I don't know.
Comic Book Store Owner: Now make like my pants and split!
'Tis the Fifteenth Season - S15-E7
Krusty: So, in the spirit of the Christmas season, start shopping! And for every dollar spent on Krusty merchandise, I will be nice to a sick kid. For legal purposes, sick kids may include hookers with a cold.
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer