Lust usually means sexual craving, Worthy means = of worth / valuable, so when they say (which is NOT common) she's lustworthy they're referring that she's really sexy he's trustworthy, he's worth trusting As Gail morse said you should definitely not say this to a girl :)

It is a slang word, personally I would recommend you not try to add this word to your active vocabulary. As a middle aged woman I would find it off putting. Hope that helps. http://www.urbandictionary.com/define.php?term=lustworthy lustworthy One (typically a girl) who is deemed worthy of another's (typically a guy) lust by some third party (typically the guy's best friend) "Dude You Idiot, I Can't Believe You Dated That Chick For Three Months!" "I Know Man; She Totally Isn't Lustworthy.