Belle & Sebastian give good instrumentals. This cut from their Legal Man EP is a fine example.
It is more notable, however, for its title, which is both naughty and nonsensical. I have a pretty good guess what a “dick slap” is (and Urban Dictionary is there to support that guess in graphic fashion) but I’m not sure how Judy, or anybody, can be one.
My guess is that this is a distinctly Scottish use of the phrase. Perhaps one of my many readers from across the pond can enlighten us.
Meet Me In Montauk 
Sure, happy to enlighten, mate! In Scotland, a “dick slap” is a woman so beautiful that she makes a man hit his penis to curb the erection.
Cheers!