Don't bring your guests down with songs that include reminders of infidelity, gambling, lying, drug abuse and other bad behaviors. And yes, there are still some songs to choose from after you eliminate those categories.
A few of your favorite songs may have negative lyrics or metaphors you've never quite gotten sorted out. Is "Puff the Magic Dragon" really about drug abuse? You'll like this: If you can't decipher the lyrics well enough to know that the song has a negative theme, most of your guests probably won't either, so go ahead and use it. Just avoid obvious mood assassins.