erm... hehe, good question!
it's like when you are being mean, but there is always a person who is MEANER than you.
e.g. Gosh, I've skipped my English class this morning and i thought my teacher would never know i wasn't there. But she got us a pop quiz and took it as a roll call... glarhhhh... it's truly like 道高一尺魔高一丈!