I'm not sure why condoms were on my list of things you could never market using social media, since, obviously, you can; you just need a moderately naughty idea, a gangsta rapper, his bodacious wife, and a small dose of topical anesthetic. On that note Durex has introduced a new Facebook app to help couples "sync up" their lovemaking by choosing the right song. Playing on the tagline for the new Performax condom brand -- which is designed "to speed her up and slow him down" with a numbing benzocaine lubricant among other features -- the Facebook app asks couples …