If you come to our house anytime soon, please know that use of the word "poopyface" will land you in an instant time out.  Ages after Martin's Uncles Mike and Jeff taught Martin the word, he's officially banned from it's use.  I started by telling him it isn't a nice word and that he could only use it with Uncles.  Then, I told him that he shouldn't use it and he cleverly prefaced it with "not" (as in "you're not a poopyface") so that he could continue saying it while not actually saying anything bad.  When I told him that he could no longer use it in any sentences ever (and after 10 minutes of discussion on what sentences are and why we use them), it only served to encourage his free applications of the word.  Finally, I told him that I didn't want to hear it anymore and that if I did, he'd have to have a timeout.  Ten timeouts later, I told him that he should use some other words instead.  I suggested the word "turkeyneck" and encouraged him to come up with some ideas of his own.  So far, he's come up with:

Shampoo: As in "Hey shampoo.  You're a shampoo."  I'm guessing it was chosen for the close relation of the ending of the word to his newly banned phrase.
Blonzy: A word of his own creation.  Must be very closely related to "shampoo" because it is used in sentences such as "Hey blonzy.  You're a blonzy."

I think his apparent talent for creating new words and word usage is probably hereditary, passed down through the men in our family.  Although I have no scientific proof that this is genetic, I do have examples from both sides of our family.

Grandpa Pat
Deedle Doodle: Used in sentences such as "How's your deedle doodle?", often replacing common questions like "How are you doing?" or "How've you been?"
Mush: Also known as your mouth.  May have second-generation German influences.
Sophienuts: A pet name for Sophie, happily adopted by Martin.

Grandpa Marty
Melvin: Commonly used in place of a person's given name.
Homer: May often replace Melvin.
Clarence: A variation on Homer.
Headball: May be used as a noun or a verb, as in "He's a real headball" or "Let's headball it".
Electric Headball: An extreme form of your standard headball.

I know it's only a matter of time before any of his new terms are going to wear on my nerves. With Martin's genetic makeup, I can see that I may be headed for an uphill battle filled with creative license.