Milhouse Doesn't Live Here Anymore - S15-E12
Apu: Attention American bar devils: it's our anniversary. Free drinks for everyone.
Homer: That's great! I'm honored to drink to Apu and, uh, Apulina. You know, Marge and I have an anniversary coming up.
Apu: I have given Manjula many gifts, including a bouquet of flowers, diamond earrings, and we're going to see Paris... Hilton, in Paris... Texas, on our way to Paris... France.
I, (Annoyed Grunt)-bot - S15-E9
Robot Rumble Announcer #2: And the winner is nature's greatest killing machine, man! [Audience boos.] Show me where in the rule book that it says a human can't be a robot.
Robot Rumble Announcer #1: Right here: Rule 1.
Milhouse Doesn't Live Here Anymore - S15-E12
Groundskeeper Willie: Brothers and sisters are natural enemies. Like Englishmen and Scots. Or Welshmen and Scots. Or Japanese and Scots. Or Scots and other Scots. Damn Scots, they ruined Scotland!
Skinner: You Scots sure are a contentious people.
Groundskeeper Willie: You just made an enemy for life.
I, (Annoyed Grunt)-bot - S15-E9
Robot Rumble Announcer #1: There's no love lost between these emotionless devices.
Marge vs. Singles, Seniors, Childless Couples and Teens, and Gays - S15-E8
[Bart and Lisa are fighting over the television remote and land on an episode of "King of the Hill"].
Hank Hill: Bobby, I got propane in my urethra.
'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