As a novice mechanic who is no stranger to rookie mistakes; I'm curious if any of you guys have some absolute whoppers you'd like to share. Whether it's something you did yourself or just witnessed, lets hear it in full shameful / embarrassing detail.
My second time cutting and installing hydraulic hoses on a pair of Ultegra R8000 levers (Di2), I had the dealer manual open and was following along step-by-step just to be safe. I installed the barbs and olives and began to tighten the last flange-bolt to spec which seemed to bottom out before being fully seated. I removed it to inspect the threads and then pulled the end of the hose out of the lever to get a look at the olive. To my surprise there were now TWO olives on the hose (UH OH). The levers I had were configued as "easy hose joint system" as written in the manual which has an olive pre-installed under each flange-bolt. I was following the directions for the non-easy joint configuration by mistake. (the directions for easy joint are in a separate section after the steps for the standard install)
I went to remove the hose from the first lever I finished and it would not come free. It took a pair of pliers and an impressive amount of force to free the hose. Inside, to my horror, I saw one olive smushed half way into another. No way in hell those were going to pop out. The next 15 minutes was spent bending and scratching away at them with a small flathead and praying to god for the threads to be ok. They finally came out in four pieces and by some miracle the threads were in good shape.