My definition of activist is someone who personally acts to improve a situation or issue. Some people wave banners and get ignored, others set examples. I think the best way as to not appear crazy and to be taken seriously is to set a sensible example, don't scream or tie yourself to buildings etc but make logical steps to achieve your goals!
I influence people every day by gentle words of advice, or by examples and have 'created' many new recyclers and spiritual thinkers! Hopefully they don't think I'm crazy, though I do joke about it often enough!