Humourless? Us? Here? Naw! Just tell you you're telling a joke first, that's all! Bob Hope himself always did it (or else he wouldn't be funny!) Or provide a laugh track like telibision does (or else it wouldn't be funny!) But no, we be humourous!
But TELLING you that I'm telling a joke takes all the fun out of it! When you go to a party, do you stand up and say to the crowd "Hey, I'm going to tell a joke now. It's REALLY funny. Trust me."
Or do you just launch into your joke, funny story, or bon mot and let the chips fall where they may?