I think its come from the fact that teachers are being approached by teenagers and being asked how they should choke someone during sex, because they think its a normal thing everyone does. Not something some consenting people do.
Also there have been several high profile cases of woman being strangled to death and the men getting off with light sentences because they say it was a consensual sex game.

Maybe they should carry union jacks and Wear balaclavas because the police refuse to arrest anyone dressed like that