[quote="Simba the Lion King"]BTW, Pumbaa DID get hurt when he and Timon got slammed into the tree and fell out of it, but why not the other times, such as with the porcupine quills and the bees?[/quote]
Well, Julie Skywalker answered the part about the bees, but Timon got the porcupine quills because they were playing a game of "Bobbing for Porcupines". In the movie, we are never shown how the game was played, though it sounds like it resembles the game of "Bobbing for apples" so substitute the apples for porcupines. Anyway, its purpose was to show Timon was initially getting tired of playing games before playing another round of "Bowling for Buzzards" which for comedic reasons actually did change their lives contrary to what Timon said.
And kudos to you mentioning the "Stand by Me" video; it's funny to see Pumbaa get hurt, but it depends on the execution of the situation.