What is the worst opening in chess?

I think it's the grav

1. e4

The opening played by the worst player

I'll give a serious answer 1f3, the Barnes attack.  It is named after English master Thomas Wilson Barnes who used the Barnes defense: 1 e3 f6 to beat Paul Morphy repeatedly. AFAIK the only player with a winning record against Morphy..    He had solid lines prepped, Morphy wanted to punish the dumb opening and gets himself in trouble: http://www.chessgames.com/perl/chessgame?gid=1266586

1. g4 is the worst first move according to Stockfish.

sodium attack, kandas opening, amar opening and ware opening

King's Gambit, bishop counter gambit accepted:

Scandinavian defense, Lindermann bongcloud attack:

Grob's attack, fools mate gambit:

Parham Attack, Epaulette Variation.

1. g4 e5 2. f3 Qh4++

This. 

Probably anything I would do would be considered really bad.

The worst opening is one where you have no clue how to proceed in the middlegame.  While 1 a4 or 1 b4 are less likely to get you to a good middlegame position where you have a clear plan of attack, those moves do NOT lose the game for you and a player who knows what kinds of attacking positions can arise from them is better off than someone who blindly plays 1 e4, 2 Bc4 without realizing the point is to attack f7 or someone who plays the London Opening 1 d4 2 Nf3 3 Bf4 because he's heard Carlsen has played it so it must be good to play, right? - even though he has no clue of where the game should proceed from there.

The purpose of the opening is to reach a playable middlegame, one that has possibilities you can see.

The awnser is the resignation gambit played by Magnus Carlsen against ding Liren in the semifinals of chessable 

1.f3 is the worst first move. 

The bongcloud

London or the Italian with 4. d3

Barnes attack 1f3 e4 2kf2

Terrible opening for anyone who isn’t Carlson

Caro-Kann, Accelerated Panov, Pseudo-Scandinavia Variation. Believe it or not this is a real thing