A while ago with some plot or whatever you like to call it, you could get beans I think it was, with that bean you could temp. steal somebody's avatar, though it would show pilfered when you did.
Because of the whole Obelisk thingy, the Awakened won and one of their boons is called LOL AVIES! it lasts for 7 days and lets you pilfer any avatar and use it... except for TNT's obvs.
And it shows pilfered, because it's not real... also obvs.
Winning as part of the "Thieves Guild" gives you this boon as well. It lasts until the next round starts and then you get to choose a new faction to battle with.
Make sure if you are battling with a faction that you win over 10 times (Any level - easy, medium, hard. I do twenty just to be sure) so if that faction wins then you get the site theme, avatar and your pick of their boons.