The Great Achievements Brainstorming Thread

League used to have an "Achievements" tab on the far right side of the client, that was unfortunately never used. However, I think Achievements, if managed properly, wouldn't be a bad thing for the game. They have already been (pseudo) implemented in the past with the Freljord events and now with the Team Builder icons.

That being said, we should keep in mind the reason Riot never went through with Achievements in the first place: they were afraid that people would ruin games by going out of their way to get them, ruining games for others in the process. Any achievements we come up with should be achievable in the course of normal gameplay (or so rare that they could only really happen by coincidence or random luck).

What ideas do you have?