Whats the worst opening ?
Serious answer: anything that relies on a cheap trick, because if you keep relying on the same slightly-unsound trick (and losing all your games against people who don't fall into the trap) then you're not learning anything, and there is a ceiling on your future progress (in rating terms, at the point where half your opponents know the trap, but you're not actually progressing anyway even before that).
Specific answer: for me it's a toss-up between the Fried Liver (I'm embarrassed when an opponent forces me into using it), and the Wayward Queen. Of the two, the wayward queen at least has the positive side of being rather fun to defend, and creating a lot of tactical fireworks. I have been known to resign on sight of an approaching attempted fried liver because it's so boring.
That's not how most people use the word "worst".
Wayward queen suck, but fried liver is working great at 800. Even if they don`t fall for it. You will then end up in an equal position.
The kings opening (after the kings pawn moves to d3/e3, the king goes to d/e2
so like the bongcloud but worse
Worst opening move: Most sources say g4, but I'd argue it's f3. This move opens a path to your king, does nothing to claim any important spaces on the board, and severely impedes your own development by blocking the g-knight's good square.
Worst opening in general: Wayward Queen. You're just asking to be bullied around the board with basic developing moves from your opponent, making no progress whatsoever.