Slightly gay sounding way of pronouncing man bitch. A response to a male (possibly gay) friend who keeps going on about how hot he/someone else is and what girls he could shag if he wanted to. Or who makes bitchy comments about someone elses appearance.
An affectionate term...
(Has 3 syllables, say: 'Man-Bee-AAHch!')
'And like, omg - Jennifer has gotten soooo fat over summer!'
'Oooh, you Man Beeatch!!'