A prestigious private school in Perth says it had no choice but to ban a "dangerous" fad.

Clint Testa, Trinity College's head of Year 7, recently sent students a message voicing his concerns for what he described as a culture of disrespectful behaviour.

Top of his list was a growing trend of boys "tapping their friends" in the testicles "with the back of their hands".

Testa said the prank was far more serious than simply mucking around.

"It was a difficult conversation to have with 180 13-year-old boys, but I impressed upon them the dangers associated with this bit of ‘fun’ and that not only can it lead to some serious short-term pain, but can also result in some serious long-term consequences,” he told The West Australian.

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The act, colloquially called "sack tapping", is when someone tries to flick or slap a boy's groin with the back of their hand.

Chevron Right Icon 'It was a difficult conversation to have with 180 13-year-old boys.'

Australian Medical Association of WA council of general practice chairman Simon Torvaldsen told the publication a student would have to hit "pretty hard" to cause long-term damage.

But he conceded it was better to nip the behaviour in the bud before the students get older.

“It’s important that schools do educate kids about what is appropriate behaviour and what’s not - and going up to other people and whacking them in the groin is not appropriate behaviour in our society.

“Better to eliminate it at Year 7.”

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