For me, it's social dancing, specifically West Coast Swing. Because while there is just social dancing, and some who only do it, there's a bit of a culture of competition, and it has its own governing body for determining where you place in competitions, and when it does sound like a cult when described.
BJJ is notorious for this
Many martial arts have a heavy lifestyle component to them, so they feel kind of culty to people who compartmentalize those bits of their life and other parts. But if you use your martial art as meditation or spiritual practice, you do you.