As my Mother always used to say:

The wind will change and you'll stick like that! - This phrase is great for when your little darling is insisting on making hideous faces which are curdling the cat's milk. It's also useful to combat a sulk, when a the child is frowning or glaring, though when in this sort of mood, a child is less likely to heed the warning. Most effective when used outdoors.

Drink any more coke and you'll go off pop! - Ideal for saving your child from tooth decay and excessive flatulence, but may fuel playground myths about fizzy sweets and carbonated drinks.

Do you want {insert threat of your choice here}? - Most effective if used with preschoolers who have yet to learn about the concept of sarcasm.

Margaretting - To bestow upon each generation of a family a name they will never use.

Rudgewick - The snarl of hair and soap that has to be regularly pulled from the plug-hole of the bath in any house where a long-haired person lives (the action of clearing out the Rudgewick from the plug-hole is always accompanied by a sneer of revultion)

In Life*, there are many hundreds of common experiences, feelings, situations and even objects which we all know and recognize, but for which no words exist.
On the other hand, the world is littered with thousands of spare words which spend their time doing nothing but loafing about on signposts pointing at places.
Our job, as we see it, is to get these words down off the signposts and into the mouths of babes and sucklings and so on, where they can start earning their keep in everyday conversation and make a more positive contribution to society.

*And, indeed, in Liff

Sandwich bread: square
Sandwich chicken: round?