If I am playing ti boy, megaman.  What about if I am wearing my earbuds and listening to the music of the ti boy?

1) Depends where you live
2) If you have it in your pocket and live in a safe area, 0.01% chances
3) Same if about everyone in the subway got an iPod/calc/other expensive device
4) Otherwise, 99% chances. In such case you better off hiding your expensive stuff from people's eyes as much as possible.

That stuff happens incredibly fast (although I think it's much worse at school). In Montreal street someone was walking in the streets with his iPod in his hands and a thief who passed by just punched him and stole his iPod in the meantime before running away.

I did see people steal stuff from people backpack before even if the person was wearing his backpack and didn't notice. In rough areas though some thieves are more violent and will literally remove the calc from your hands or attack you.

In my area it is generally kinda fine unless you are a pizza deliverer in St-Jean Crysostome. Schools are the worst place to bring expensive stuff in, here, though.

I think it's pretty ironic that your username is RobberGuy, but I really don't think anyone would go through the trouble just to acquire your calc. Unless it's filled with military secrets.

It depends. If the thief knows a lot about electronic devices, then he might be aware that a TI-83+ costs $80-140. Otherwise he'll just think it's a simple calc (after all there are scientific calcs coming from weird companies that sells for $10). But even then, there are people who steal items at the dollar store here, so you never know. There are people who steal bus stop signs.

Also it depends of countries and regions. If you live in South Bronx, Detroit, East St-Louis, Montréal-Nord or south of Juju's school, then you're at higher risk. But in my city it's worse if you're in a school. What gets stolen the most in hi schools here are bicycles, TI-83+/84+ calcs, iPods and in elementary school outdoor clothes. At one hi school where I went, there were students selling used calcs to others for $50, when in fact those calcs were stolen from other school students.

Everyone simply puts their names on the back of the calc, and everytime someone leaves it behind, it gets taken to the lost stuff, where they can get their calculator back.

Might just be because you are required to have a 83+ or a 84+ on my school.

Guys occassionally steal calcs at my school, but not much. If I'm not using my calc it usually is in my backpack (read: never :p). I think a CX is more likely to be stolen tho due to the fancy looks it's got.

Outside of school, your calc should be relatively safe. Thieves are usually only interested in more common devices such as cell phones and MP3 players.
In school it's a different story, but you can often avoid people stealing your calc by putting a cheap calc in your backpack, in a place you'll see before you see your expensive graphing calc. People often assume everyone has only got 1 calc unless they know you.