In reply to james oswald:
> Any science or psychology behind it? Is it just used to draw attention to themselves?
It's theatre (in the broad sense of knowing people are watching you).
Gives a public form to an individual experience. Raises the complex issue of the grey line of where the individual ends and society begins. The strange truth that doing the same thing alone or with others watching is in fact a "different" experience.
Similar to the reason they encourage footballers to symbollically copulate when they score - in football the homoerotic component is more significant.
I noticed in Dave Mac.'s (no personal criticism intended, just inevitability) new video trailer he screams a lot "giving form" to his huge efforts, his suffering creating a "sign" for hardness. Often this is encouraged by video makers by showing approval when screams, or simply editing in all the screamy bits and cutting the long mute sequences.
Porn is another example - the need to articulate with vocal expressions and the same tendency to exagerate.
In the end it wears out, folk become enured. Art is based on narrative. Screaming and rolling around means nothing in the end.