Ah, I see.
Well, actually, I have no clue what that means, but it does answer my question.
Ooops, sorry! I missed your original question.
As Arcade22 said, it's Ayumu Kasuga, nicknamed "Osaka", from the Japanese 4-panel comic strip (and later cartoon) called Azumanga Daioh.
Azumanga Daioh is essentially a Japanese Peanuts set in high school. Osaka herself is the slightly-cracked space cadet type. She's holding knives there for...well, the particular image my avatar is from has an even more complex backstory. But the knives are a reference to the moment the characters were having a sleep-away study camp, and Osaka decides to wake her teacher (chaperoning the study camp) by taking a frying pan from the kitchen and banging on it.
Osaka, whether because she was half asleep or just because she was Osaka, ended up grabbing a knife from the kitchen instead, which alarmed the teacher quite a bit when she awoke to see a cheerfully smiling Osaka approaching her with a giant knife, though things were soon sorted out without any injury.
The strip where all the above took place was published a couple years before the Sasebo slashing where the girl who became famous on the internet as "Nevada-tan" killed a classmate. Which is why Osaka and the knife was supposed to be funny, rather than being an offensive and horrifying joke in the wake of a tragedy.
