Shirt gnomes refer to the creatures that sneak into peoples', primarily females', closets and steal the bottom halves of t-shirts, tank tops, etc., leaving the shirt with only the top half intact and the bottom half missing, thus showing a region of midriff. These gnomes are the primary party responsible for the new "crop top" epidemic facing the United States today.
These creatures are thought to be gnomenoid in physiology, but their diets are that which we have never seen before. The digestive tract in most mammals simply cannot create the enzymes necessary to break down fabrics such as cottons and polyesters. However, shirt gnomes, which are thought to be closely related to sock gnomes, seem to have the ability to synthesize such enzymes using outside technologies. This allows them to have a food source with very little competition. The creatures were facing a widespread extinction since the 1980's, but upon synthesizing this new enzyme as well as moving to human-inhabited indoor arenas to avoid predation, have regained a hold of their small, but now thriving, population.
"My closet seems to have been targeted by the shirt gnomes, Dr. Falardio, all of my once very reasonable tops have been torn into crop tops." - females everywhere, 16-25 years of age.