Nonwords...I have been making a little list of nonexistent "words" that I've heard people say. (Very compulsive of me, I know.) I can tell from their pronunciation exactly how they think the word is actually spelled, too. (The example sentence isn't necessarily what the speaker originally said.)
subline: "That was a subline experience."
paradign: "We're working from a different paradign here."
pneumonics: "I used pneumonics to remember it."
expedentially: "The problem grows expedentially larger each day."
Amsel Adams: (No sentence necessary.)
ideal (used in place of "idea"): "I had an ideal that it would turn out like this."