It is argued, on the basis of first principles and a case example, that 'leakage' of advertising messages beyond the target audience can generate negative reactions when 'activists' in an accidentally addressed 'meta-audience' exert 'social pressure' on the advertiser's 'micro and macro-audiences', inflicting 'collateral damage' on the advertiser in various ways. Examination of published data from industry sources shows that activists are a small sub-set of the meta-audience, but it is argued that their potential to reduce the long-term advertising effectiveness of some advertising campaigns is an issue for advertising managers and planners. Analysis of hitherto unpublished data yields a profile of one type of activist: those who complained about television advertising between 1996 and 1998. They belong to homogeneous social sub-groups that are geographically and demographically distinct from the general population, not least in conforming to the notorious north-south divide in Britain. It is proposed that this first-ever research-based profile of complainants offers a factual basis on which prudent advertising planners can predict the risk of collateral damage, and plan to minimise it by avoiding pre-disposing creative tactics or media schedules.