Maybe you were adopted.
4 seconds sound clip from the Back to the Future movie soundboard.
You can hear this line at 00:56:19 in the Blu-ray version of the movie.
Quote context
[...]
- Very funny. You guys are being real mature.
- Jesus, didn't that guy ever have hair?
- Shape up, man. You're a slacker. Do you want to be a slacker for the rest of your life?
- No.
[...]