Coke is a hard one to kick. Never addicted to it, but I did it 3 times and I will be completely honest- if you laid a line out in front of me, I would have a hard time resisting, though I don't think I would do it.
Pot, going to be impossible for me to stop, especially because I use it medicinally.
Tobacco... I've already dealt with a collapsed lung, and chronic bronchitis- if I haven't quit smoking because of that, no hope I guess... I wish they had a nicotine mouth spray, or some sort of nicotine pill. Chantix is known to cause aneurysms... and I don't know if the other shit works...
Addiction is a hell of a drug.