Road: I bought my whole Ultegra 8050 Di2 groupies, and the day before I had my appt to have it installed at the LBS, my mechanical shift cable had snapped for the rear, leaving me either with 52x11 or 36x11. I guess the cables somehow knew they were no longer needed and decided to give me a big parting “FU”. Aside from that I’ve only cursed roadside a few times when my GP4000sii tire sidewalls decided to succumb to small rocks on the road, and when I ran over a nice piece of glass with my brand new GP4000 a few months ago and ruined it beyond repair (the center moulding mark wasn’t even worn off yet!!!)
MTB: Bent RD hanger 3x, bent Eagle GX Derailleur Body and had to replace the entire thing, the air piston or whatnot in the fork was defective and was warranty replaced, Eagle GX chain snapped leaving me walking back to the car, and when the chain snapped it also bent some of my cassette cogs which had to be bent back in with a hammer and punch.