What I don't like is ads that use psychological devices to try to get me to buy their product. I also don't like ads that are a distraction of the content I'm trying to consume. So when playing a game, if the ad scroll at the bottom of the screen is flashy, I can't easily play that game so I give up. Now an ad that shows on a loading screen may be more acceptable, as long as the contents of the ad aren't something that would get me fired if someone at work sees it.
I also hate that ads have to have their own javascript in it. The ad networks should provide a safe canned set of functions that they control, and not serve up anything that an ad customer submits.
Finally, if I'm already doing research for something (such as browsing through the Bose headphones site), I don't want to see ads for those same headphones that I already researched, following me around on all the web pages I visit. It just really feels like someone is stalking me. Or look through a site like rvtrader, then when you look up the weather the next day you see a bunch of camper ads. Again, stalking. It's gotten to the point where I constantly browse in a private browsing tab (yes, there are ways they can still track me, but they aren't as obvious about it).