Sorry that I don’t have a specific story that qualifies as a certified horrorshow, but I have had enough issues with voice nav apps (“in 1/2 mile, make a u-turn”) that I’m sure that some of you have some good ones.
The Garmin in my folks’ rental car gave them directions which included driving over a bridge that was closed long-term for major repairs. Fortunately I knew the area and told them an alternate route (with the Garmin shouting “Turn around! Turn around!” until it recalibrated).
Not a nightmare scenario, but a disappointment. I got a Tom Tom device for father’s day a number of years ago, with a Darth Vader voice file. The disappointment is that the Tom Tom doesn’t announce when it is recalculating the route when I make a different turn than recommended, because I really wanted to hear Darth say “I find your lack of faith . . . disturbing”.
My “smartphone”‘s voice navigation system (we call it "Bitchin’ Betty") must have been cloned from a New York taxi driver’s brain, since it has sent me on wild goose chases that involved insane, circuitous detours rather than logical routes. The last time was when it decided that a Best Buy was located out in the countryside miles from human habitation.
It also loudly and irritatingly beeps at me if I exceed the speed limit by the tiniest amount.
Siri tried to take me to Switzerland once. If I’d had more time, I’d have at least tried to read far enough to figure out just where the bridge across the Atlantic is.
I have the voice part of the nav turned off. I don’t find it to be useful.
On the other hand the voice activated dialling in the car has tried to call my boss of bosses who I would never call, instead of my mother.
Not a horror story, but…using a GPS in the State of Hawaii can cause much merriment. Have you ever heard it try to pronounce a name like “Kalanianaole”?
Once we actually backed up the car and drove by a street a second time, just to hear the GPS voice mangle a street name all over again while we laughed ourselves sick. I guess if that had caused an accident, it would be a horror story.
Ours is pretty bad at Spanish or Spanish-derived names. Probably not as amusingly hyper-local as Hawaii.
The GPS once decided that the fastest way to a KOA-style (not actually KOA) campground in central Pennsylvania was not to take the actual highways the somewhat extra distance but to try and use a bunch of farm roads. I gave up and turned around once I got to the broken-down car being used as a perch by two or three bemused cats.
My parents tell a story of trying to get somewhere in the Four Corners region and the GPS kept trying to have them turn down dirt roads on the Navajo reservation. Again, there was a perfectly good paved highway, but the dirt road was “shorter.”
Also, in one of the units we hadn’t updated the maps because the cost of an update would be as much as a better unit with newer technology. It was so old that it didn’t know I-99 existed and kept telling me to just turn off in the middle of the highway to get to US-220.
A minor irritation was when I was driving my mother and her bf downtown and his TomTom had me going in the wrong direction. I kept thinking it was the wrong way but since I wasn’t sure what side of town I wanted I listened to it. It had me drive 4 miles the wrong way, and then make a u-turn and then go back the way I thought we should be going.
A major irritation was OnStar. I took the wrong exit off 495 and the next thing I knew I was in DC- confirmed when I saw the Washington Monument on my left. I was totally lost and OnStar was no help as it would tell me to turn blocks too late, or onto streets I couldn’t find. I was going in circles, and finally had to call and get a live person to get me out of there.
There is another street in the town where I live that has the same name as my street. Every GPS sends people to the other street. Work people show up late, food delivery gets it wrong - I even had trouble finding my house when I was house hunting because I kept getting directions to the other street. I tell everybody who comes to visit to follow the directions I give them - but they never listen and end up over there instead of here.
My GPS once directed me to turn onto the Federated States of Micronesia. It was actually a Farm to Market(FM) road out in Texas.
My Nuvi once had a fit while I was driving to the top of Mt. Washington. The car icon started desperately turning from side to side while the voice shouted, “Recalculating! Recalculating! Please drive to the highlighted route!!!”
I always figured that it was afraid of heights… 
We were driving through the Tejon pass to visit some friends up in Tehachapi, and the highway was pretty well defined - it hugged the mountain on the left, and the right side was either valley or grasslands. There were exits from the highway maybe every 4 or 5 miles, but that’s it.
Siri FREAKED OUT. She kept telling us to “keep left” for no reason. “In 10 miles, keep left.” “In 3 miles, keep left.” “In 1/2 mile, keep left.” 1/2 mile later, at a completely nondescript section of highway with no offramp, cross-street, or anything else - “Keep left.” Ooookay Siri. And immediately after we had passed that invisible merger (???) it would start again. “In 15 miles, keep left.”
We figured she had gotten drunk after a bad fight with the concept of right. “Fukkkken make sure ya don’ go right. Right’ll jus’ break your fukkken heart, keep, keep lef’. Right is a COCK.”
A rental car GPS once advised my husband to make a left turn on the Oakland Bay Bridge, just after paying the toll. Not really a nightmare because we just laughed and mocked it mercilessly. But if we were stupid enough to obey it and drive off the side of the bridge it would have been a nightmare.
I hate voice navigation, be it a device or my passenger. I want to look at a map, dammit. So I always do. I keep it in my head, maybe jot down the streets where I need to turn (in large black writing that doesn’t require readers; guess how that came about?).
So we’re visiting a town where none of us have ever been. We’re looking for Target. Dad finds it on his GPS. I look at the google map. We get in the car and I’m driving. I pull out of the drive and turn to the north where I see the street I need two blocks up.
“Take the next right”
“She says to turn right.”
“Well, I’m going straight because I see where I need to be ahead of me.”
“She says turn right”
“But I’m driving and I see the street dead ahead.”
“I rented the car. Turn right.”
I turn right. Immediately I hear “Take the next right”
So I take the next right.
I smile. Mom’s smirking.
“Take the next right”
Now we’re both laughing and in unison with the hated GPS we chime “Take the next right.”
So we’re headed right where I was headed the first time.
By the end of those three days, my brother and I were threatening to have a contest to see who could run over it the most times.
Thought of another one. I used to briefly live in an apartment complex where the GPS could not figure out how to get in. It kept trying to go in circles looking for roads and entry points that didn’t actually exist.
Odd…mine does say that exact thing when I miss a turn/have to detour.
I had a garmin that would occasionally lose it’s mind - twice directed me into a parking lot, then do a U-turn and back out in a different direction. Would have been more amusing if I was at all familiar with the area - I wasn’t.
Nightmare is a strong word. But Google maps did (maybe still does?) have an annoying feature that malfunctioned badly for me a number of times. I don’t know how it works behind the scenes, but it looked like it sometimes knew where individual buildings are, and if the building was closer to a different road than the formal street address it would consider that the destination.
Maybe that is a heuristic that is sometimes useful, but it failed badly for finding a friend’s apartment building which was right next to the interstate. It insisted that I had arrived while flying down I-75 at 65mph. And of course any attempt to leave the interstate was rewarded with instructions to get back on, until I pulled over and manually figured out the rest of the way.
They seem to have a thing against left turns. My aunt jokes they were programmed by the post office. I get the “go up and U-turn” instead of left turn fairly often, but ignore it.
I once had one send me to completely the wrong shopping center for a store (the correct one was less than a mile away, but much smaller). Guess it just had the wrong address. That store has never been in the shopping center it specified (I remember when that SC was built).
Occasionally had one think I was on the service road instead of main highway. Mispronunciation of names fairly common.
On the whole, though I think they’ve been improving over the years.
I use the nav program Waze. It’s pretty amusing that it consistently refers to the Veteran’s Administration (V.A) Hospital as the “Virginia” Hospital.
Also when navigating to the Dane County Airport, it will try steering you out into (as far as I can fell because I can’t follow the instructions to the end) the middle of the main runway rather than to the terminal.
I was in Houston going from my motel to the USS Texas/San Jacinto Monument, the GPS led me onto a ferry. As I was waiting for the ferry to finish loading and take off, the GPS kept telling me to ‘Turn Left’. Um, I’m not driving.
It took me back to the motel on a different route over some gigantic bridge with yellow beams (Fred Hartman?) and never used the ferry again.