One of the best pranks is to install the startup app then set it to start the blue lcd program. As soon as the victim turns off the calculator and turns it back on, the screen is blue. You cannot quit the program, and if you take out the triple a's, the screen still stays blue.
you have to leave the calc turned on, then take the aaa batteries out. After re-inserting them and turning it on, you need to take the BLUELCD program out of the startup app.
BTW, does anyone have the BLUELCD program? TIcalc.org seems to have taken it out of their archives.