Cut off your nose to spite your face
Meaning
Disadvantage yourself in order to do harm to an adversary.
Origin
The Oxford Dictionary of Quotations lists this proverb as "mid 16th century - mid 14th century in French". I wouldn't doubt them but the earliest citation I can find in print is much later. Grose's 1796 edition of the 'Classical Dictionary of the Vulgar Tongue' explains it thus:
"He cut off his nose to be revenged of his face. Said of one who, to be revenged on his neighbour, has materially injured himself."