I would say its the french defence
most hated chess openings

IMO openings that can potentially be the most hated :
a : 1) e4
1)...c5 2) c3 because even if we don't lose, it can be very difficult to win with Black
1)...e5 2) Nf3 Nc6 3) Bc4 Bc5 4) b4 because a strong gambit and since "we don't really want to waste time studying anything other than Ruy Lopez", it can be annoying.
b : 1) d4 d5
London system and Coll system of course but probably also :
2) f4 Nf6 3) e3 because it can be difficult to win with Black.
2) e4 dxe4 3) Nc3 Nf6 4) f3 exf3 5) Nxf3 because not very pleasant to play with Black due to the potential danger that this opening can create.

Easy!!! The London System. I used to say the Berlin Lopez but now its definitely the London. Seems as if I'm always playing someone where I feel thats the only opening he knows and I don't know how to play against it. Lost many a game.

people who play the anti sicilians, anti benonis, exchance french/slav, or london
like grow up and stop playing for tricks. if not that then at least try to win as white

Anti-Sicilians. This just doesn't make sense, you are offered to play an amazingly fun, complex middlegame and than you choose some random boring line like the Alapin.
The London, but it's not that I don't like to play against it, but I just don't get why people would play such a boring system. You don't get any experience in new structures and you allow black to get an absolutely fine position.
And lastly the English, but this is just my personal opinion. The english is an absolutely fine opening but I find it really hard to play as black. I never get positions I like and the positions are often really passive for black.

falkbeer counter gambit... can't wait to be able to play it myself with the rare, but DEVASTATING (but I won 1 each 5.Bc4, 5.Bb5 and 5.Nf3 games and lost 1 each playing 5.Nc3 and 5.fxe5??)
falkbeer nimzowitsch marshall countergambit. OH THE CARNAGE!
this is the MAIN LINE:

Any opening that you ruins your plans. Like I want to play Scotch game, but many of my opponents ruin all my plans with their C5. So I hate it a bit
I think that you should respect them, but I gennerally agree. I like to play the tennison gambit, but my opponents always seem to play the reti or the nimzowich. Nimzowich black mustang is so boring!
I hate most gambits, but the Staunton Gambit in particular. Wouldja just let me set up my little stonewall please?
I hate PLAYING the toothless pawn pushing stonewall, but the staunton does make it even worse.
Add another vote for gambit coward poodles... I mean frenchies, then add pirc, modern and Owen's. COME OUT AND FIGHT YA COWARDS!
I hate the french much LESS now that i've discovered the alapin diemer having ALWAYS done poorly against it, but am satisfied that my results are up a % now at 45:48 with the alapin diemer which ACCIDENTALLY led me to destroying caros with the mieses gambit. Caros aren't used to Bxf7+ pin breaks and are lambs to the slaughter. I was TRYING and failing with the maroczy fantasy.
As a current kings gambiteer who can't wait to up his attacking game with the double danish & 2x Goering, I'm very happy getting BDG semi-open f files and trashing fellow scandinavians with the gedult BDG making for a full BDG system against french, caro and scandinavians. The alapin is the ONLY gambit i have a losing record with. You can't exploit that GM approved +1 pawn if your opponent mates you before move 20, and 14% of my wins are that fast.
Glad to see too that my King's gambits are annoying. Try the falkbeer counter or 2.Be7 to trade for the Nf3 knight and box whites rook in with a ...Qh4+ followup. I hate that.
As much as people like to trash talk gambits, it's nice to FINALLY hear people hate them the same way i despise pawn pushing wussy POSITIONAL hypermoderns and closed games.
I have no fear of the alekhine myself and find it easy to beat. I have a winning record with I forgot what I used to play, but am punishing it again with the castle snatching krejcik "gambit". The 4 pawns never interested me. I like piece based solutions, not pawn based. I hate pawns!
don't forget the "everybody's gotta lose" english! The best line I've found is the c6 caro variation, but it's so rare, it's not even worth studying when I have to learn an entire repertoire to ditch the skankanavian