noun: An imaginary device that a man apparently wears when he gets obsessed with a woman that he is having sex with; causing him to ignore other parts of his life, or the fact that the woman is not good for him.
The phrase uses beaver, a slang term for female genitals. and refers to horse blinkers (blinders) which are a device used to stop cart pulling horses becoming distracted.
adj: Beaver Blinkered
John: Have you heard from Tommy recently?
Don: Not much at all since Tracy came on the scene.
John: Ah, he'll have his Beaver Blinkers on, he can't see anything but pussy right now...