Ok I'm going to say it.  There is a word I absolutely can not say without laughing.  POOP.  Today with friends I attempted to diagram exactly why it is that this word is funny.  I decided that the letters themselves have a lot to do with it.  Explosive P's and the liquid U in the middle definitely play their part.  And then the feeling of the word as it leaves your lips, having a satisfying lingering effect, making your mouth pucker and release into, even if it is unintentional, a smile upon your face.  And after all of this dissection of phonetics and mechanics of spelling, I thought aw hell poop is just funny!