I'd say there's two kinds of answers to this question.
The first category are the lolcows who are actually worth hating because they've done shit that's pretty fucking despicable by any standard.
The second category are the insufferable assholes who have a knack for making you temporarily "mad at the internet" more often than other lolcows.
The only ones I can truly hate are the legit sickos like Nick Bate, Yaniv, Peter Bright (hell, pretty much any pedo lolcow), Randy Stair, Zoe Quinn, Brenton Tarrant, or the zoosadists, or the ones in the Community Watch thread who actively commit ideologically motivated violent crimes like Antifa, Atomwaffen, and the Black Israelites.
I'd say that Bob Chipman, Olivia Hill, Jake Alley, Amanda Winn-Lee, Nick Fuentes, ContraPoints, Vaush, Vox Day, the incel communities, Andrew Dobson, Boogie, and most of BreadTube all show a very unique talent for being those insufferable assholes of the highest order.
Sargon, Romeo Rose, and ADF also have that same level of being utterly insufferable, but are all so hilariously pathetic it becomes comical, while guys like Chipman or Alley are the really mundane kind of pathetic and that just makes it worse on a very banal level.
Sargon deserves credit for destroying an entire political party by himself, while ADF and Romeo Rose are like walking political cartoon characters.
Zoe Quinn used to be in the "insufferable asshole" camp before Alec Holowa died. Now she's firmly in the "actually worth hating" group since she drove an innocent man to commit suicide based entirely on false accusations.