Skiaddict, rock-throwing on Shabbos is disapproved of because under the circumstances that is not the way to deal with the problem (you are not going to fix the frei majority this way). However, it is not something which is absolutely out of the wack — it is just not good under the circumstances. Besides, some hold that those chiloni people are tinokos she’nishbu. Plus, I have a shaila about the permissibility of the rock-throwing vis-a-vis Hilchos Shabbos.
PBA and Sam2, where is the mekor that if two people walk into a place and see someone eating treif (or wearing a mini-skirt), that it’s loshon hora to exchage a comment about it between themselves?