Not just bad movies are known for one clip, here are some good movies that conjure a specific scene when people talk about them in mixed company.
The scene: “You talking to me?”
Why you should watch it: It's a classic film, if you really haven't seen it, you should watch it now.
Planet of the Apes:
The scene: “Take your stinking paws off me, you damn dirty ape!”
The scene: “Soylent Green is people!”
Why you should watch it: This one is the most questionably good movie on the list, but it's another Heston classic.
The scene: “Heeeeeere's Johny!”
The scene: “I'm as mad as hell, and I'm not going to take this anymore!”