Tom Meagher, whose wife Jill was murdered in Australia in 2012, said it's dangerous to defend the likes of convicted rapist Ched Evans, while decrying 'more violent' rapists.
Tom is working with the White Ribbon campaign to end violence against women.
Figures show that almost half of Irish women have been sexually harassed and 42% have experienced some form of sexual abuse or assault in their lifetime.
Tom's wife Jill was raped and murdered by Adrian Bayley in Melbourne in 2012.
Speaking on the Ray D'Arcy Show on Today FM, Tom said all rape is rape, and all men should call out their friends when speaking ill of women.
"I think it's how we separate the idea of the friendly abuser and the monster. People who rush to defend people like Ched Evans might be the first people to violently condemn people like [Jill's murderer] Adrian Bayley.
"If we're talking about degrees of rape, we're discounting the pain of the victim," he said.
"I think it's grossly irresponsible to suggest that we can draw a difference between a 'good rape' and a 'bad rape'."
He said small actions, such as objecting to demeaning comments about women in social situations, can have a large impact.
White Ribbon is an international campaign seeking to end violence against women by men. It encourages men themselves to be at the forefront of the campaign, and to neither make excuses for it, or remain silent about it.
It began in Canada in the late 1980s following a massacre which saw 14 women killed.
You can find out more about the campaign at whiteribbon.ie.