Know your limits. Don't pretend that you can handle something that is too much for you just to look cool, but you can get there by doing a little each day.
For that matter, don't take shortcuts to skip the harder parts of improving yourself, because you'll only be cheating yourself and others. Someone's going to find out eventually, you'll eventually hit a point where skimping out on the hard parts will come back to hurt you, and you'll look even worse off than if you just accepted your limitations and did the work.
If you invite your friend to do an activity and they don't want to partake in it, don't force them into doing it anyway. You're effectively not giving them a choice by doing so.
Big-Lipped Alligator Moment: Near the end of the episode, the air from SpongeBob's anchor arms begin to randomly shift to different parts of his body before exploding completely. Beyond outing SpongeBob as a fraud, this particular moment never gets brought up again.
Strawman Has a Point: While opting out of exercise altogether wasn't the solution, it's understandable why SpongeBob didn't want any part of Sandy's training regime, as it quickly escalated from out of his depth to flat-out dangerous.
Squidward the Unfriendly Ghost:
Alternative Character Interpretation: When Squidward confessed that he faked being a ghost the whole time, did SpongeBob really assume he was in denial of his death, or did he just claim this while wanting to get back at him for tricking him and Patrick into becoming his slaves?
SpongeBob and Patrick standing next to the coffin and saying "okay, get in" is a popular reaction image to someone doing something incredibly stupid and the like.
The ending scene where SpongeBob and Patrick send Squidward up to the "Great Beyond" in a bubble gained traction as a way to give tributes to recently deceased celebrities. Including Hillenberg himself.
