Maybe if you ate 20lbs of apples at once.

that's why I don't drink the whole glass of water

Everything is poisonous in high enough quantities. It would take a lot of apples for the seeds to become an issue.

It would take around 100 apples to poison an adult human, assuming you crushed all of the seeds. It's reccommended that you core apples if you're juicing them and serving it to children; otherwise it's harmelss.