Adjective
caustic - Sarcastic or severely critical, often in a hurtful or biting manner; or able to burn or corrode organic tissue, typically referring to chemicals or substances.
The caustic chemical spilled onto the floor and quickly started to eat away at the floor surface.
arbitrary - Based on random choice or personal whim, rather than any reason or system
She felt that when the judges chose her competitor as winner of the debate, that the decision was totally arbitrary, and didn't recognize how well she had really done.