For me it's working on cars and trucks that I absolutely can't stand working on. I would rather work on the smallest skidsteer or mini excavator before working on cars and trucks.
I recently changed the water pump on my GM van. Easy right? No drain plug. Then try as I might I could not get the fan clutch off the hub. Mechanic friend came over and we tried every trick in the book including a claw hammer and a baseball bat used in creative ways. Thing would not budge. Finally took the whole pump out fan and all in one piece.
Chucked it up in the vise to pull harder on the hub (using the baseball bat as a cheater, aluminum one without an end cap) and that nut came right off easy, and the end of the bat which I was set to pull overhead for maximum oomph, hit me right on top of the head.
I should have sent it to the car mechanic before even looking at it, but I thought, this will be easy....