Cocaine and crack are cocaine; cystal meth is
methamphetamine, a totally different drug.
Crack is much more dangerous than cocaine; its
potential for addiction is so bad, one use can cause
it. And it's awful for your body in all ways.
Crystal meth is so bad, we call it the "meth monster".
I have seen people who were kind, nice, and
dependable, turn into theives, whores, and worse
for it. It is terribly addictive, and messes up your
heart (your heart literally "jumps" when you take
meth, tearing it), brain, bones, etc. One way to tell
meth addicts, aside from the speed bumps another
answerer mentioned, is by the fact that they lose
their teeth. Also weight, time, and their minds.
Unfortunately, had friends who fell into these traps,
now lost to us.