A person who is afraid to get with a girl because he is with his bros or a person who won't do fun shit because they are afraid they will get in trouble.
A reference to the male ass. Since a female vagina has a vertical slit, much like the ass, it is easy to see where the term derives it's meaning. It can also refer to the anus of a man, though this would be erroneous as the anus looks nothing like a vagina unless both have been dilated, in which case both are gaping and disgusting.