I even have a name for it!
From an article from Australia:
A new study has found that anonymity gives people the same feeling of abandon as power and alcohol intoxication. Researchers at Northwestern University in the US found that all three states led to extreme behaviour — both good and bad.
"Although these pathways appear to be unrelated on the surface, they all lead to disinhibited states through a common psychological and neurological mechanism," said Jacob Hirsh of the university's Kellogg School of Management. Dr Hirsh's colleague Professor Adam Galinsky said the loss of inhibition led to "significant behavioural consequences".