I used to think the word "memento" was spelled "momento," as in, a trinket by which to remember the moment. I'm convinced many others have made this mistake. What are your eggcorns? John used to think "bedraggled" was pronounced "bed-raggled," as in, all raggled from bed.
Also: An undisclosed number of people, not knowing what a French exit is, have assumed it to be a sex act. Praytell, if it were, what would it be?