Like any profession, there are good and bad mechanics out there. The worst experience I've ever had with one was when I paid a shop to change my transmission fluid. The only problem was while they took the old fluid out, they didn't put new fluid in. (It happens way more than you think.)
I figured something was wrong when my shifter kept popping into neutral on the road. When I brought the car back to the shop, the mechanic had the audacity to blame it on me. I'll never forget what he said: "Are you SURE you know how to drive stick, sir?"
That's about the most galling thing you can say to a car guy, I think. He may as well have said "Are you SURE you know how to satisfy your wife, sir?"
Anyway, what's the worst thing a mechanic has said to you? It could be an insult, or bad news, or awful advice, or something you knew was just plain wrong, like saying you needed headlight fluid. Vent away in Kinja below.
Image source The U.S. National Archives