When a person has become so infatuated with his girlfriend that he no longer has time for his friends.
Dom: Where's Jack?
Pete:He's being birdgay.
Dan: Jack is birdgay.
A man who spends an excessive amount of time with his significant other and/or instead of spending time with friends.
Adam is a fucking birdgay.
Someone who spends their time in a desperate attempt to pull non-interested girls by spending time with them laughing at their non-funny jokes and generally brown-nosing them rather than hanging out with their mates (if they have any) until everyone becomes so sick of them that they are shunned by soceity.
This aggravates said mates, prompting them to call the person a 'bird gay'.
Actions and hand signals are also appropriate
"olly is being such a bird gay, as if hes gonna get pussy from her"