Depends on what time of the day it happens.
If it's closer to school ending, paint.
Start of the day? Boiling water. That shit will dry, and if you're burnt you get to leave school. Dur.
Megatron. Fuck that Chuck Norris bullshit.
Besides, robots.
Swords can "cut" *through* water but your arm can't. You'd swing it pathetically slowly.