Brain herpes is something unpleasant that you haven't thought of in a while that pops into your head every once in a while. You can't unsee it, unhear it, etc. Once you contract a brain herpes, it is with you for life.
Examples of brain herpes include: goatse, that fucking Barbie Girl song, the image of when you walked in on your parents mid-coitus, etc.
by Pho King Guy June 02, 2010