Undecorable

As an incubator of table-cloth scrawlers, New York is enormously prolific—you see tag-ends of verse, sketches, names, and undecorable hieroglyphics in restaurant after restaurant, provided you beat the waiter to the cloth.

Source: wiktionary

Sponge painting radiators is a simple but effective way to decorate something which is usually undecorable!

Source: wiktionary

Moreover, were a foreign government or national involved in the disappearance of a Brit on British soil, the diplomatic implications would be undecorable.

Source: wiktionary