the worst day as a driver, that I remember, was a 8:40 to 11:30pm night in 2014. I finished my route around 6:45pm and was sent to help a driver out who had a breakdown.
I took off something like 25 or 30 stops but they were in a town which I had never delivered.
The kicker was it was a torrential rainstorm at that point and visibility was very low.. I did not have a flashlight with me (stupid) and the UPS trucks (851***) headlights were useless as any I've ever seen. Roads were ponding if not flooding. Could not see any house numbers whatsoever, so I had to drive a little, stop get out and look, rinse/repeat.
The horror was around 9pm, having to deliver one of those giant EZ closets, I think it was 8 huge pcs., down a 200-300 foot driveway. I couldn't risk backing down. The customer did not know whether to be angry or feel sorry for me. It took several trips down that damn driveway and probably 10 minutes and I am still drying off from that night.