Family-Unfriendly Aesop aside, when the kid on the field trip wets himself, Billy Madison decides to keep him from being totally embarrassed. How? By pretending he wet himself as well. Billy could've humiliated the kid further, but decided to take the other route.
The ending of the film where Billy decides he'd like to be a teacher, and where he and Veronica kiss passionately.
Not only that, but the guy who's been helping Billy subvert Eric's plotting gets what he deserves as well:
Billy: Anyways, um, this hotel stuff really isn't for me, so I've decided to step down as chairman of Madison Hotels... and give the company to Carl.
It was kind of sweet during the climax when, even after Eric's Villainous Breakdown has him pulling a gun and the audience appears to clear out entirely, Billy sees his two friends still sitting there, waiting for him.
Billy calling someone he used to pick on in high school to apologise for his nastiness. The man is so touched he calls off his vendetta against Billy and even saves his life.