COCKBLOCKER

1. (noun) a female friend who accompanies another female friend to planned meetings with a male peer, to ensure that the sista does not get into trouble; 
2. (Noun) a male who interferes with another male's attempt to freak the woman whom the former either wishes to protect as a friend, or is already pursuing himself; 
3. (Verb) to cockblock: basically, to interfere, by way of one's mere presence, with the attempt of one person to freak another

 Jill "Jane, I really need you to come along tonight as my cockblocker so I don't do anything I would later regret. 
Jane "Sure"