It's a sad tale, because humor invariably involves risk. When someone tries to be funny and fails, it makes the rest of the world --particularly the nonprofit fundraising world, which is already prone to an excess of seriousness -- chicken out (with all due respect to the chicken) and stick to the tearjerker appeals, which can be real yawners.
When done right, humor is a great way to make donors smile -- and then give. But how to do it right? Here's a helpful article, "When Humor Can Be Very Effective in Fundraising Marketing Campaigns," by MP Mueller, for the Association of Fundraising Professionals.