Something you hate about an otherwise great movie

[Wingnut]

This scene from Back to the Future:

Diner owner (Mr. Carruthers?) (DO) : So kid, you gonna order something or not?
Marty: Yeah, I'll have a "Tab".
DO: You can't have a tab unless you order something.
Marty: Then gimme a "Pepsi Free"
DO: If you want a Pepsi, pal, you're gonna pay for it!
Marty: Just give me something without any sugar in it...


"Pepsi Free" was caffiene-free, not sugar-free. I know there's no other way to have that joke come across, but it's still lame.