(n.) A diminutive, insignificant, or presumptuous person.

JD a nobody a nothing boldface brat brazenface chutzpanik cipher common man dummy elf enfant terrible figurehead gamin holy terror hussy imp insignificancy jackstraw juvenile delinquent lightweight little fellow little guy little monkey malapert man of straw mediocrity minx nebbish nobody nobody one knows nonentity nothing nullity obscurity pip-squeak puck punk punk kid pup puppy runt saucebox scrub shrimp small fry small potato small potatoes smart aleck smart-ass smarty smarty-pants spoiled brat squirt squit swaggerer upstart urchin whiffet wise guy wise-ass zero zilch