Most unsound opening?

The Benko gambit is the most sound true gambit that has ever existed. Answering the #1: Obviously 1.f3 e5 2.g4. (fool's mate)

definitely the Englund Gambit

I would say either Englund gambit (d4 e5), or Duras gambit (e4 f5)

a : The Latvian Gambit because refuted.

b : Defense Damiano is very bad but in theory it is not refuted.

1) e4 e5 2) Nf3 f6 3) Nxe5 the Black player is not obliged to play 3)...fxe5, he can play 3)...Qe7 then there is no refutation.

c : https://youtu.be/6QHpJTrIenk Chess Openings: Kasparov's Refutation of The Marshall Defense!!

Ok but the problem is Black can play 1) d4 d5 2) c4 Nf6 3) cxd5 and now 3)...c6 and probably also 3)...e6 then there is no refutation.

d : 1) Nf3 e5 2) Nxe5 it's a stup*d opening but normaly there is no refutation.

e : Bongcloud Attack, Noble Prize of the troll ok but normaly there is no refutation.

There is no opening that is "refuted", probably excluding 1.f3 e5 2.g4.

There are many openings which are unsound, or even objecively outright losing. But at the practical level, all of them are playable if the opponent is tactically blind (pretty much the case for most low-rated players).