B cells are a specific type of white blood cell called a lymphocyte. Other types of lymphocytes include T cells and natural killer cells. B cells develop from stem cells in bone marrow. They remain in the bone marrow until they become mature.
Infantile behavior is something the masses are taught to exemplify since childhood. As adults they (mostly Betas) are encouraged to have sexual relations with multiple partners.
Quite a lot are made up, that is part of the fun really. I have never heard cockwomble in the wild personally but I can see it is a fairly humourous insult. The Wombles are a kid's puppet / stop-motion show from the 70s, they are little furry creatures who live in Wimbledon Common. A cock is a penis of course.