Longest win streak and lose streak.
I'm on my longest right now -- 11. I won 6 ranked, then 2 normals I played because I was afraid the streak would end, then 3 more ranked. All as Karma and Master Yi with one Janna game. My previous longest was 10, but mostly normals.
I won games with some odd teammate picks too: a Jayce jungle, a Yasuo jungle, and supporting an AP Ryze bot. Aaaaand two of my games I played mid, which used to be (still is?) my worst role!
My longest losing streak was 14 (all ranked). I'd like to beat it, but right now I'm scared to even queue.
I lost SO MANY Karma games this season trying to build her like a traditional support. Now I just build damage. And I don't waste gold on Tear, I just tolerate being low often and I take the mastery for 5% health/mana back on kill or assist - actually useful!
EDIT: It stopped at 11.