A crude sex act involving a man with a mustache, an oreo cookie and a vagina. First the oreo cookie is inserted in the vagina. Next the man with the mustache feeds from the vagina as best he can and tries to ingest the oreo cookie. If all is successful, then the act is considered a pustacheo.
man one- "Hey I just walked in on Hitler last night with his mistress! He was eating an oreo cookie out of her vagina! I should try that sometime!"