As quoted from the website: http://americandad.w...wiki/Stan_Smith :
"Stan attended John DeLorean High School in the late 1970s and early 1980s. A very unpopular student, Stan was scrawny and had horrible acne, which caused him to be nicknamed "The Penis".... It is revealed in "Chimdale" that in an effort to get rid of his acne, he took part in testing of an experimental acne treatment. The treatment caused all his hair to fall out, and he has worn a toupee ever since. Up until this episode, he didn't think anyone knew. The family told him that it was obvious (other than Steve who had no idea). His co-workers still have no idea though."
Further episode detail here ---> http://americandad.w...m/wiki/Chimdale .
***UPDATE: You can watch the whole episode here but you have to try "Hulu-Plus" for free and cancel before you get billed:
Edited by TreatAcne, 28 August 2012 - 01:01 PM.