One time, we picked up a Xamarin project and both Android and iOS teams had to pick a developer to handle it. After talking over it with my iOS bro, I decided that I hate C# far too much to start a project on this, even though I wanted a new experience, so iOS bro took over it. I got handed another iOS project in the meantime. iOS bro decides to take a free week from work after like a month or so of working on that project.

GUESS WHO DECIDED TO COME OVER AND WORK WITH US THAT WEEK? THE OWNERS OF THE PROJECT (they were handling the API). Guess who had to drop all projects at once and work for a whole week on a project he had no idea about in a programming language he only had a remote idea about? THIS GUY.

So, aside from the fact that I had no idea what I was doing, I also had the pressure of the owners working right next to me (they were cool people, but it's still a stress). That week really raised my stress level through the roof, as I doubted myself everyday that I would be able to be productive on that project. I got myself a free week too after that.

But yeah, this experience really made me doubt my skills as a programmer, as Xamarin was supposed to be just a cross-platform way of developing an app.

All in all, I've never had to work on that project again... but it was still an "I can't fucking believe it" moment when, one month-ish later, the project was to be scrapped and reprogrammed on ye olde Swift.

Me, the only iOS dev at work one day, and colleague (who we'll call AndroidBoy), the only Android dev at work that same day (he's been working with us for less than two months). There was a change in one of the jsons we received from the server: instead of receiving a list, we now received a dictionary with strings as keys and lists as values. My iOS colleague had already made this modification on our parse function the day before.

AndroidBoy: "Hey what happened with the json?"
Me: "Oh, well instead of parsing a list, we'll parse a dictionary and get the list from each key. You basically have to do the same thing, only this time the lists are organized into categories."
AndroidBoy: "Oh, ok. But I don't know how to parse a dictionary while using Retrofit." (Context: Retrofit is a framework for request handling - correct me if I am mistaken, that's just what I've been told)
Me: "Sucks, dude, can't help ya. I've never worked with that and don't have that much exp. with Android."

I go out for a cigarette break. When I return, AndroidBoy is nowhere to be seen and suddenly I can't seem to get that data in my app. AndroidBoy comes in from the room where the backend colleagues work.

AndroidBoy: "Solved it!"
Me: "Solved what?"
AndroidBoy: "I told them to change back to a list and just put the key inside the objects of the list."

... he used the precious time of the backend colleagues to change the thing back hust because he was too lazy to search how to parse a dictionary. I was so amazed by his answer, that I didn't know whether to laugh, scream at him or punch him in the face. Not to mention the fact that now I had to revert just so he could avoid that extra work.