Lorraine Baines: Marty? Why are you so nervous?
Marty McFly: Lorraine. Have you ever been in a situation where you knew you had to act a certain way, but when you got there, you didn't know if you could go through with it?
Lorraine Baines: You mean like how you're supposed to act on a first date?
Marty McFly: [stammering] Sort of.
Lorraine Baines: I think I know exactly what you mean. You know what I do in those situations?
Marty McFly: You do? What?
Lorraine Baines: I don't worry.
[kisses him hard]
Lorraine Baines: [Lorraine stops and pulls back, Marty is freaking out]
Lorraine Baines: This is all wrong. I don't know what it is. But when I kiss you, it's like I'm kissing... my brother. I guess that doesn't make any sense, does it?
Marty McFly: Believe me, it makes perfect sense.