One word I never get right the first time is "sarcophagus". It always comes out "car-sophagus"--like the love child of an automobile and an esophagus. Good thing it's not a part of my daily vernacular now, but when I was teaching fifth and sixth graders a unit on ancient Egyptian civilization, I used it quite a bit.
There was one day I took two empty cardboard guitar cases (my hubby plays) that were the perfect size and shape for a 5th grader to fit into as a sarcophagus. The two teams had to choose one of their members to be the mummy. The others wrapped him in toilet paper. I was cheering for each team, "Hurry! Wrap him up and put him in the carsophagus! Go! Go!"