Zack: What's wrong, Lisa?
Lisa: This ring put a green stain on my finger!
Zack: Why would it do that?
Lisa: Because it's not real gold, DUH!
Zack: Well, maybe it's just yours. (the rest of the gang reveals green marks after removing their rings) Maybe it's just ours.
(more students show up with green marks on their fingers)
Nerd: There he is!
Zack: Maybe it's just everybody's!