noun
Derogatory term for someone who lives off others, especially an adult who depends on parents for financial support. The literal image is 'shin gnawer', suggesting a pest that clings and feeds.
彼は三十歳になっても親のすねかじりだ。
He's still a freeloader living off his parents even at thirty.
いつまでもすねかじりをし
I can't keep being a sponger forever.
Rare kanji form using 臑, a variant of 脛.
寄生虫 literally means 'parasite' and can be used metaphorically for a person who lives off others, but it is more biological and less colloquial than すねかじり.
ヒモ is slang for a man who lives off a woman, often in a romantic context, whereas すねかじり is broader and typically refers to depending on parents.
From 脛 (すね, shin) + かじり (齧り, gnawing), literally 'shin gnawer'. The image is of a small animal or pest clinging to someone's leg and gnawing, metaphorically extended to a person who lives off others.