In-game irritations, big or small, in no particular order. Feel free to toss in.
When you're about two mobs away from a boss and your team-up blows their signature.
Hightown, melee character, brick-wall cops that encircle the boss and make a slugger's life that much more fun in patrols. It's hardly my fault their job is less important because I can throw a cement truck through three buildings without losing velocity.
Having 1-3 of a ton of different uniques, just shy of freeing up precious storage space. I'd be tickled if they'd change the trade-ins to 3-5 of any unique, not just duplicates.