Probably losing a villager I really loved, Kyle. He was my BF for a really long time, and I must have missed his ping and didn't hear any rumors... You know when you're talking to one villager and another comes up pinging but you can't get through the dialogue fast enough? I think that's what happened, so one day I logged on and he was just GONE. It was super sad because even though he wasn't a dreamie, we was actually an OG villager, his house was in the PERFECT place and he was a total cutie... He also went perfect to balance out Skye and Freya so it was just a really crappy situation. I got over it eventually, and like with most of my BF's who disappeared in previous towns I had his picture out in my living room. =[
In Fall 2013 Erik moved out of my town - he was my favourite. There was an event the day before so I missed that chance for him to ping me. In hindsight, it affected me way more than it should have, but I was so sad and didn't play again for weeks.
I haven't had him in town since, and would definitely move him in if I didn't have so many deer already.
At least I have his picture displayed at home
I'm glad they give you ten days notice in the Welcome Amiibo update instead of five. It's saved me from more heartbreak.
When I returned to the game after not playing for a few months, I found out that Cherry had moved. I was very much not happy. I do have her in my new town though. ^_^
When Tutu put her house exactly on top of my only 5 purple roses I had at the time. And I had no access to trading forums or anything to buy some more.
Two months after the release I found the 10th random villager in the wrong spot. At the time I didn't know the rules about the 10th villager. I was very upset but over time I figure out how to work around Sydney house.
Both Marshal and Punchy left my town during my hiatus (logged in once, noticed Punchy was gone, logged out, came back, Marshal was gone too). These were my two favorite villagers so I was really hesitant to come back to ACNL since I don't like having a village without them and cycling through 16 villagers is tedious.