A Question About San Francisco

Allegedly, San Francisco is the world's only "flesh friendly" metropolis.  But is it?  I ask because I've also read that there is a possibility that a naturist might be detained by the police if he/she strays out of the Castro district.  It seems that there is also some discomfort on part of the local Castro populous, and further, that there are some restrictions on visiting parks, etc.  Is there anyone with "real-world" experience walking it buff in S.F. who can shed light on the Do's and Don'ts when visiting that fine city?