In the first "street dancing" scene (the one in which Kelly accompanies Ozone and Turbo to the beach), the audience watching the dancing is comprised of surfers and beach bums. In said audience, we see a man in a black singlet clapping with the music. This man is Jean-Claude Van Damme in his first on-screen appearance. According to Van Damme, he tried hard to draw attention to himself by jumping in the air and doing flips but they were not included in the film.
First feature film of rapper Ice-T - two of his early instrumental rap songs were used (Tibetan Jam and Reckless); the producers later used Tibetan Jam in the film Missing in Action (1984) where it was used as background music.
In the second dance battle scene in the club, Ice-T can clearly be seen rapping/talking into the microphone in the background yet we do not hear him at all. All that can be heard is music and the main characters dialog.
Towards the end of the movie when Kelly and Ozone are arguing at Venice Beach, the last shot of that scene as they are walking away; Ozone says, "I want to show you what real dancing is about." You can see that Ozone's lips don't move, but you can still hear him say something.