First off I can't say how incredible reassuring it is to hear I'm not the only one who makes these kind of stupid impulsive mistakes. Even though I've never made the same one twice I do feel like I make lots of new ones all the time.
The stupidist and more expensive mistake I ever made was buying a '95 Saab convertible. I was straight out of school, had a little bonus for a job I was starting shortly and convinced that my time had finally come. I looked at a bunch of different ones but all the cars in my price range were pretty beat. Then, I found one in Boston (first mistake) from a used car dealer I got a bad vibe from (second mistake). I did have it inspected but not by a Saab mechanic or even an foreign car specailist (HUGE mistake). I even let muself overlook the odd spots on the carfax because the car was so sexy (triple black leather with every option).
The car is beautiful and I slap down my bank check the same day.
In the course of the next nine months I replaced:
Timing Chain (requiring the removal of the engine)
Transmission
Alternator (for Saab convertible this is a big money item)
all hoses and belts
windshield (fortunately covered by insurence)
Head gasket and all other upper engine gaskets
rear brakes (calipers, rotors and all)
ECU (factory recall, didn't have to pay after I made a scene at the dealer)
And too many little things to count. I was too busy keeping my high-pressure new job in a terrible economy to do any of the work myself and newer Saabs are very very difficult to self-service anyway. Needless to say, I took a huge beating. I managed to sue the dealer for a couple grand but I'll never see the majority of that money again.
I found out later on that the car had been stolen and taken on a high speed chase before sitting in the impound for a year. This explained the new tires and paint and why a car with 65,000 miles would have such a bad service record. It was whipped.
The only bright spot in the whole story is that I bought my 420sel and read several mechanical textbooks in order to learn how to service it. I've gotten pretty good and the new car is running great, plus I've learned some really valuable life lessons.
I console myself by saying at least it wasn't some horrible property deal I stumbled into, that would've bankrupted me.