And I don't mean the obvious ones. Like stacking killing when the stack isn't nearly tight enough. OR self reporting in the first round and accusing someone…not realizing that they will get voted off the next round. (Assuming Confirm Ejects is on.) Just the things that maybe somewhat intelligent people may have done in the first few times they played, but quickly realized how dumb it was.
For me, the biggest one is imposters who IMMEDIATELY sabotage lights, and then kill in electrical. So, when pretty much the whole damn lobby is running into the room, they are killing in it.
I also had an imposter partner get caught killing in a room with 4 crewmates around, then get pissed at me for not double killing. And no, it was not 4 on 2 at that point. It was early in the game. It was 7 on 2. So when he obviously got caught, he did the baby standby of ratting me out. Still don't get why he thought us both killing when there still would have been 2 crewmates left alive would have been a good idea.
And yes, not so coincidentally, this was during a sabotage that he called, and in the room to fix the sabotage. Which is why even if there WERE only 2 people in there, I would not have double killed because 1. I knew others would come and 2. I sure as hell wasn't expecting him to kill so I wasn't prepared to kill myself. Early round sabotages are to gain trust. Or to get away by sabotaging as far away from the body as possible.
What else is there? Things like not practicing the running sabotage. (And sadly, voters who don't put any weight on the knowledge that someone was running, stopped, then a sabotage was called, and they started running again and therefore don't vote for them.)
Another one I just thought of are the last surviving crewmates (like 3) not realizing just how much time you have to fix O2 sabotage and splitting up rather than all doing one together and then all going down to the other one. Or worse, when it is Comms. Can't tell you how many games I've lost as a crewmate when we started a round 3 on 1, with maybe 2 tasks left between us (I always finish mine way before others) and they split up to do Comms rather than us all sticking together to do the tasks. As if comms matter at all wen you are down to one task and should be able to remember it. But even if it is O2, there is still plenty of time on all maps to get to both O2 panels