MIT offers some useful advice on what to do if you witness offensive behaviour.

Strategies in the moment

• Name or acknowledge an offence
• Point to the ‘elephant in the room’
• Interrupt the behaviour
• Publicly support an aggrieved person
• Use body language to show disapproval
• Use humour (with care)
• Encourage dialogue
• Help calm strong feelings
• Call for help

Strategies after the fact

• Privately support an upset person
• Talk privately with the person responsible for the inappropriate behaviour
• Report the incident, with or without name