Hypnosis has been around for thousands of years (that we have a record of). For much of that time, it was only practiced in a very formal, ritualized fashion. In the past 100 years, it started out as a medical treatment, then diverged from that. From there it split into hypnotherapy and stage hypnosis, both of which were pretty rigidly defined and predictable.
But over the last decade or so, a new generation of hypnotists has broken out of those boxes and taken hypnosis to a new and completely uncontrolled environment, the "street". In much the same way you might see a magician performing in park, these practioners of street hypnosis perform with no stage and no rehearsal. It's new, fresh and often unpredictable.
In person, it's like running across a musician or a street magician. Fairs and festivals, boardwalks, events, beaches, malls and other public places are becoming regular haunts for street hypnotists.
Barring running across a street hypnotist in person, YouTube has a lot of videos. As with anything on YouTube, some are great, some are interesting, some are fake and some are completely inexplicable.