Never done it myself, but I know enough to tell you most of those stories about people ripping their own eyeballs out, eating their own faces etc. is total bullshit.
If it sounds impossible it probably is, and with the amount of fat and muscle keeping your eye balls inside of your head removing them with your bear hands seems pretty impossible to me. This is of course all media hype coupled with criminals blaming their irrational behavior on drugs even when that wasn't the case.
Phencyclidine is not very common, only in certain areas like Washington DC, LA, and Philadelphia among others.
http://faculty.washington.edu/chudler/pcp.html
The only substance with a known significant link to increased incidents of violent behavior is and always has been alcohol.