Lazily copy/pasting one frame.

Agreed. And even when I do I tend to get little amount done because of this bad habit- checking previous time for a whole minute.

That happened to me in my last animation. I had to redo a scene, which meant I failed to meet the contest deadline

DEFINITELY one of my fatal flaws!!!

I think I'm guilty of all of these at one time or another,
Another thing I do is forget to double check my camera settings leading to flicker, color shift, or worse.
I just had to re-shoot a scene because I just set the exposure to the camera's meter without checking it, only to get into my software and find out that the higlights were completly blown out.

“But the enterprise in which I’m about to embark on is fraught with imminent peril.”

This has been happening to me recently: I'll catch minor mistakes in my animations and tell myself that I'll just fix it in post. I spent too much time during THAC in post because I kept trying to fix things.

TwoGuysBrickfilms Youtube Channel

I am sadly guilty of almost all the bad habits in this thread...
Apart from the ones already mentioned, one of my biggest problems is leaving sticky tack littering my sets, often after characters move. It just sort of trails behind them, and I don't feel like removing it.

In the past, bumping the webcam was a big problem for me. In some cases, it was impossible to put exactly where it
was. So I created a rig for it that could attach to the base plate.

Ahhh yes especially with dark grey bricks, they're so reflective and it's really annoying