na-adjective, noun
utterly lacking; hopeless; useless; poor
Emphatic, colloquial expression meaning completely devoid of skill or ability. Often used self-deprecatingly or in light criticism. Rare term; more common in spoken or casual written Japanese.
See also: から下手
私は料理がからっ下手で、目玉焼きすら焦がしてしまう。
I'm utterly hopeless at cooking; I even burn fried eggs.
He's a terrible singer, but for some reason he's popular.
Formed from the prefix からっ (emphatic, from 空 meaning 'empty') attached to 下手 (へた, 'unskillful'), with the reading へた changing to ぺた for phonetic emphasis. The exact derivation is uncertain, but it likely originated as a colloquial intensifier.