var pattern = /^[a-z][a-z0-9_]*(\.[a-z0-9_]+)+[0-9a-z_]$/i;
 
[
  "me.unfollowers.droid",
  "me_.unfollowers.droid",
  "me._unfollowers.droid",
  "me.unfo11llowers.droid",
  "me11.unfollowers.droid",
  "m11e.unfollowers.droid",
  "1me.unfollowers.droid",
  "me.unfollowers23.droid",
  "me.unfollowers.droid23d",
  "me.unfollowers_.droid",
  "me.unfollowers._droid",
  "me.unfollowers_._droid",
  "me.unfollowers.droid_",
  "me.unfollowers.droid32",
  "me.unfollowers.droid/",
  "me:.unfollowers.droid",
  ":me.unfollowers.droid",
  "me.unfollowers.dro;id",
  "me.unfollowe^rs.droid",
  "me.unfollowers.droid.",
  "me.unfollowers..droid",
  "me.unfollowers.droid._",
  "me.unfollowers.11212",
  "me.1.unfollowers.11212",
  "me..unfollowers.11212",
  "abc",
  "abc.",
  ".abc"
].forEach(function(pkg) {
    console.log('[' + (pattern.test(pkg) ? '✔' : '✘') + ']\t' + pkg);
});