what is the worst chess opening on the first move

I think it is F3 as it exposes the king, doesn't fight for the center and blocks the G1 knight.

The worst first move according to the engine is b4. The Grob

f3

G4 the grob.

You might think so, but according to the engine, it is worse to play the grob.

Worst for white, or worst for black?

I used to think that 1. e4 f5 was the worst black can do on the 1st move, but engines are so anti-Grob that 1.h4 g5 gets the win over that, in the "bad opening" way. Even more than that is 1.d4 g5. I guess its better to develop the B instead of the R.

Switch that last one around, and 1. g4 d5 is probably the worst position for white after just 1 move.

Or if you mean the worst move for white followed by the worst one for black, double g-pawn should get that - 1. g4 g5