горе луковое

горе луковое  {n. phr.}  {ironical}

`gor'e `lukovoe

 {literally}

Onion misery (or trouble).

1. Said abt. a luckless person who involves himself or/and others into troubles (even despite good intentions).

2. Said abt. a person who is helpless (for ex. in doing sth.).

Often said to naughty children.

Горе ты мое луковое! Ничего? сам сделать не можешь. — Poor thing! You can do nothing yourself.

 {Origin}

Most likely the 'onion' is just the way the exression sounds, apart of that it does not deal with onions at all. One of the origins mentioned is the word 'лукавый' — (sly, arch, cunning, playful, and even 'the wicked evil one'), which sounds quite the same way in Russian. Thus we have 'горе лукавое' or 'горе от лукавого' (stress on 'а') — 'a trouble caused by the wicked one' or 'an unjust trouble'.

See:

blunderer, double-trouble, muddler, sad sack

See:

 {v.} наделать дел, наломать дров