there's actually a word for this - a sniglet is defined as a word that is not in the dictionary but that should be. there are a bunch of lists of sniglets people have come up with on various websites. here are some of my favorites:
acronymnnym - a redundancy created by following an acronym with the final word of that acronym, such as ATM machine.
shuggleftulation - the actions of two people approaching, trying to get around each other, and muttering "thanks for the dance."
frust - the small line of debris that refuses to be swept onto the dust pan.