In popular mythology, Yom Kippur is the holiest day of the Jewish calendar.
In most shuls, you have to be a member (or buy a special ticket) to attend these services. Most Jews only go to shul twice a year (Rosh Hashanah and Yom Kippur) and synagogues fund themselves by selling tickets to the High Holidays.
Chabad shuls are different. Any Jew can walk into a Chabad shul without buying a ticket. And he’ll be welcomed even if he’s wearing jeans and purple hair and sporting tattoos and earrings.
So in a typical Chabad shul on Yom Kippur, at least half the crowd will be the hardcore Chabadnik in his white kittel and tallis and he’ll be praying up a storm. The mood is more upbeat than a goy would suppose for this solemn occasion. The observant Jew rejoices in Yom Kippur and embraces what it stands for — personal transformation through the forgiveness of sin and a commitment to do better.
Chabad Jews tend to be happy Jews. For most observant Jews, observing the Torah seems to be more of a burden than a blessing. For Lubavitchers, it’s more of a joy than a burden.
So in a Chabad shul on Yom Kippur, the place will typically be packed. There tends to be much less personal space in Hasidic Judaism as opposed to the Litvish variety (which is usually more restrained). The believing Jew will be happy and joyous and clapping and shouting and swaying and getting into the occasion. And then about half the crowd will be secular Jews who are rarely in shul. They will typically wear jeans or other informal wear. They will wear those cheap nylon yarmulkes. They will be looking around to find the right page in the mahzor (High Holiday prayer book). Sometimes they’ll be checking their cell phones. They’ll typically look bored and put upon and it is obvious that they can’t wait to get out of there. That the prayers mean nothing to them but they’re just showing up out of obligation.
So you’ll look around and half the crowd will be passionate about the day and the other half could not care less.