cockblocker

noun1

1. •
   (slang, vulgar) One who cockblocks; one who impedes the sexual advances of another, usually a man.

   • "What do you think of Nova?" "Well ... I guess you could say he's a cockblocker." "Shep, we don't use words like cockblocker." "Fine, then he's a ... chiseler." — 2005