2 disk games that didn't recognise your second drive
Games that forced NTSC when my TV wouldn't do it and just roll (Dynablaster, BC kid)
Games that used space as a second fire button with no option to allow one on the joystick
disk labels starting to peel off and leading to the disk jamming in the drive
games on huge numbers of disks with no logic as to the order of gameplay, leading to constant swapping
That should do for now!