Doesn't it have to do with party hopping?
Bashing is a harsh, gratuitous, predjudicial attack on a person, group or subject. It is used to imply a sense of uncompromising vehemence and bigotry about the assailant.
WIKIPEDIA
The term applies to two different types of attack: physical assault and verbal or critical assault. In the latter case, bashing is used metaphorically to indicate an attack on a subject that is of similar aggressiveness and motivation to the physical case. Topics which attract bashing tend to be personally sensitive topics for the bashers, the victims or both. They also tend to be highly partisan issues. Common areas include religion, nationality, sexuality, politics and topics of critical appraisal within fandom.