Those stereotypes of crazy cat people may have some truth to them. A Czech scientist has found that
a cat parasite causes behavioral changes in human hosts. Men infected by the toxoplasma gondii parasite tend to be "quiet, withdrawn, suspicious, jealous and dogmatic" (i.e., the typical cranky cat-owning misanthrope), whereas infected women tend to be "reckless and friendly", with slower reaction times (i.e., the typical flaky cat lady).
http://www.natur.cuni.cz/~flegr/