Ugh, lol, that is an easy one.  Without a doubt the worst significant item purchase I ever made was the Mitsubishi Mirage.  As soon as I paid it off (and I paid it off 2 years early) the transmission went out on it, and the O2 sensors as well they wanted to charge me $6000. for repairs, Which, of course,  I could not afford since I had just paid $5000 to pay the damn thing off.  I ended up selling it as junk for $650 dollars since then I caution everyone I know NOT to buy a Mitsubishi vehicle under any circumstance!