Help me solve this riddle does anyone know it?

I'm going to take a guess. There were at least 3 people around when you heard this joke and all three broke into laughter as soon as they heard it. The joke itself is not that funny.. The laughter involved is from the reaction you give when you hear it. Usually, there are two responses. The "I don't get it so I'm gonna think about it for a while and hope you explain it to me." or the "I'm going to laugh along with you so you don't think I'm stupid." In any case.. they really aren't laughing with you... they are laughing at you.