“My Best Friend’s Girl” tries to be a romantic comedy, but is too raunchy to be either romantic or comedic.  Tank (Dane Cook) has developed a certain kind of expertise with women:  he is able to completely turn them off, and be the worst date they ever had.  He has found this dubious talent to be useful when his friends are having trouble with their girlfriends.  All they have to do is arrange for them to have a date with Tank, and they look great by comparison.  Works like a charm, except when Tank tries it on his best friend’s girl (Kate Hudson), and winds up falling for her.  He’s so unpracticed at being genuine that he’s forgotten how.  Do we really want to root for such a vulgar, callous fellow? 
         By contrast, Nick (Michael Cera), the guy in “Nick and Norah’s Infinite Playlist,” is quiet, unassuming, somewhat dorky and self-absorbed, but is a really nice guy whose girlfriend has unceremoniously dumped him, though he still pines for her.  At a night club gig where his garage band is playing, Nick runs into Norah (Kat Dennings), who’s admired him from afar, but she’s been too shy to approach him, and now she’s trying not to look like a dork herself for being unattached, so she asks Nick to be her boyfriend for five minutes.  And then provides him with a long, languorous kiss.  Well, that sets our lonely boy to thinking about other possibilities, but of course the night is still young, and by the time we have roamed the streets of New York looking for lost drunk friends, we just might have a spark going here.  Much more innocent than “My Best Friend’s Girl,” and the awkwardness springs from relational ineptitude rather then cynical manipulation.  Sure, there’s some crude humor in “My Best Friend’s Girl,” but I’ll take sweet over raunchy even when I think no one else is watching.