I had a guy putting tires on one of our heavy trucks and I went out in the yard to see how he was making out just as I hear buppa-buppa-buppa-fuck!
He's broken off a 7/8" wheel stud with his fucking 1" air gun, putting the over-nut on and ugga-duggaing the fuck out of it for some goddamn reason. Shrugs his shoulders and tells me it must have been broken already (it wasn't, break was shiny all the way through). He's got another one broken off on the ground beside him. Asks me if it's ok with 8 out of 10 (on duallies, ffs). I send him home and take the drums off and pound out the studs.
It's too damn often where I spend just as much time fixing mechanic's fuckups as I would have to do it myself. Had a Deere mechanic do some insurance-funded work on a combine I blew up so we'd get warranty, I swear he didn't own a torque wrench. Had to tear it down and re-torque nearly every bolt.

