For me it was:
1. Malenia
2. Elden Beast
3. Placidusaxx
4. Maliketh
5. Margit
6. Rykard
7. Mohg
8. Astel
9. Rennala
10. Radahn
11. Morgott
12. Godfrey
13. Fortisaxx
14. Godrick
15.. Regal Ancestor Spirit
If I could put Draconic Tree Sentinel he'd be number 2 on god, **** this dude.
Oh if we want to include non-Remembrance bosses, lemme copy paste my previous list and change it:
Godskin Duo. Whoever made this boss should be fired and blacklisted from working in a video game company. Leave 'em to the fast food industry. I hate this boss more than any other boss in video game history.
Draconic Tree Sentinel. Ironically, not the one everyone hates outside of Leyndell, I fodderized that one every time somehow. But the absolute ****** in Farum Azula made me want to rip my head in two with my bare hands. Idc that he is a "normal enemy", which is bullshit, I literally respeced at Rennala twice for this enemy. Maliketh felt like a worm compared to it.
Again, not technically a boss, but the stupid Ulcerated Tree Spirit in the Haligtree, near Malenia. I actually didn't even die to it that much, but it made me more enraged than anything in Elden Ring aside from the above 2.
Omegachad Starscourge Radahn.
Radagon/Elden Beast.
Fire Giant.
Margit, The Fell Omen.
Mohg, Lord of Blood (although tbh he'd probably be number 2 if I beat him the right way instead of cheesing).
Maliketh, the Black Blade.
Godrick the Grafted.
Gigachad Godfrey/Daddy Loux.
Rennala.
Malenia (I trivialized Malenia so hard lmao).
Morgott, the Omen King
Rykard.
Pacidusax.
Regal Ancestor Spirit, Astel, and Fortissax I kinda fodderized. They didn't kill me one.