I hate knowing how much money is spent on them so that they can annoy us with every attempted second of our lives. What, you can't use that money to better pay your workers? You can't use that money to improve aspects of your company, so you're going to pay these groups of obnoxious pricks whose entire existence is to annoy people with your ads?
The ads themselves are too theatric for me to care, I can't tell you the amount of ads I've had to stomach hearing through Spotify that makes me care even less about a product. They just take turns outdoing themselves as to which ad is the dumber of the bunch that night. Even worse are the ads that try too hard to reach for something that was 'hip' to do like 5 or 10 years ago.
The lying in commercials. I've learned in life that some brands that aren't even the brand of choice, the best option available. I've been surprised on some of the things I've acquired from even dollar stores that somehow are better than the name brands.
And even then, there's still lies projected from commercials that attempt to snag you in for money.
As others have pointed out, there's a lot to hate about ads since the industry is routinely dishonest, insulting, obnoxious, deceptive, intrusive, and all manner of unpleasant. I've been adblocking religiously for most of my life for these reasons.
So I think a more interesting question might be the other way around: "What do you like about commercials?"
The only commercials I've ever liked are the ones for local small businesses. The ones with a nonexistent production budget that aren't beating the viewer over the head with blatant lies or dishonest sales tactics.
Adult Swim used to have faux-ad bumpers for the fictional business "Strickland Propane" from King of the Hill, featuring the honest-to-a-fault character Hank Hill as the spokesman, which I felt captured that vibe well.
Rhett and Link also made a funny homage to these kinds of commercials in this classic skit: https://www.youtube.com/watch?v=vnOyMSEWNTs