This episode's plot seems straightforward, but it's actually a metaphor for weed. I mean, think about it. The episode is about SpongeBob and Patrick becoming "hooked" (quite literally in this case). Mr. Krabs knows that it'll kill them, and tries to stop them, but unfortunately the two do not heed his warnings. So Krabs tries giving him an overdose of weed, with the help of Squidward of course, and that ends up making SpongeBob strip his clothes off and embarrass himself, and Patrick to become irreparably addicted (the tuna can symbolizes his state; trapped forever in a state until he receives proper help). It's one of the series' darkest episodes.