Meth addicts get fucked up faces because they engage in what is known as "picking". People who do this are known as "pickers". If you don't know, this type of drug makes you focus with incredible attention to detail to things that normally don't require that much attention. For example, scrubbing an entire floor meticulously with a toothbrush, cleaning the grout between all the tiles in the shower with a toothpick. A classic example though, is when they start looking in the mirror to try to pick at pimples. Once they get the real pimples they start scouring over their entire face and picking at every little pore, scar, and scratch. THey get obsessive and fuck up their faces by picking and picking and picking, until their faces are super fucked.