Post your opinions here! What are some fun things to do when
bored in class? 
That will depends on what you have on hand, and how creative you
are.
The standard things to do include drawing stuffs while
pretending to take down notes, reading mangas/storybooks placed
inside the textbooks, and shooting paper pieces using a rubberband
at your other classmates.
The not-so-nice things to do include throwing a marker at the
ceiling fan ( Make sure you are not close to the fan yourself ),
cutting the hair of the girl in front of you, attempting to shoot
the teacher with your paper pieces and rubberband, and playing a
PSP/NDS under your desk.
What I personally recommend when you are bored ( though not
really fun ), is to take out some homework and get something done,
especially when the teacher is going through stuffs which you are
already long done with, or take down notes and compare them with
stuffs which you already know.