Similar to the term "booze-hound" for an alcoholic, "Vaj-hound" is a term you use when referring to a male (or lesbian) who is addicted to "vajs" (vaginas). Similar to the term "man-whore".
John: "Hey Bob, I saw you messing with a new cute chick....isn't that the fourth one you've gone through this week?" Bob: "Yeah, I can't help it.....I'm just such a major vaj-hound I can't help it. I can't get enough of vaginas that I constantly have to be frogging on several different women all the time."