Most Annoying thing with steam?

the ammount of direct x install

Steam community market botters

And when they get caught they only get community market ban...
Same with cheaters in game. VAC ban should result in permanent steam ban.

The client.

i really really really miss the "visit store page" on the drop down menu after right clicking a game in your library!!!
now I have to right click, click on 'view community hub' and then I can click on 'visit store page'! annoying, specially when steam decides it doesn't want to load on the first try..

i dont like that you cant split out games from packs , i like to be able to chose what games to activate and what games to keep in my inventory ...

The API. Most of the time really slow and it lacks many possible features.

the inability to verify game files for all games in one go

Most F2P games don't stay in your library when they aren't installed, even after buying a DLC for it (Like Pinball FX2). :(

Cant trade on mobile or internet connection.

Makes me poor.

I need more advanced games categories management in my library

Prob been said, but not being able to buy multiple gifts of something at once.

try webbrowser then

iPhone app uses US store (because i'm in Mexico), but I can only buy off of the UK store (because that's where my finances are)

the inability to disable group notifications.

I'll also add inability to disable group notifications or at least be able to move them to a spot not likely to interfere with your game. I had one pop up during a game and I ended up with a game over because it covered up the spot I was in at the time.

Steam takes too much bandwidth when downloading games, causing everyone in my house to have slow internet (I have a crappy internet connection).

I passionately hate the fact that you can't hide games from your public games list.