Mooning is now illegal in Victoria with those who bare their bums facing up to two months behind bars from July 1.

The law is part of an overhaul of 50 sexual offences designed to crackdown on offensive and abusive behaviour while modernising police powers.

First-time offenders will face a maximum of two months in jail while repeat offenders face up to six months.

Changes to the Crimes Amendment (Sexual Offences) Act 2016 describes mooning as someone exposing their rear end.