The jokes that are the funniest hit closest to home. If they hit any closer, they hurt; if they hit any farther, they aren't funny. It's a fine line, and unfortunately humor IS in the mind of the receiver, so you probably will end up offending the more easily-offended people, who have a larger "bull's eye" - but you can learn to avoid them. It's telling the SECOND joke that offends the same person that's offensive... the first can often be dismissed as If they knew better. The trick is to learn to dismiss it when no offense was intended, even if some was taken.