Biatch is another way to say the word bitch. The small tweak in pronunciation gives the word emphasis or an air of humor depending on situation. The popular rapper Snoop Dogg was the first to use the term "biatch!" on the multi-platinum selling album "The Chronic". The term was further popularized in his rap classic solo album titled "Doggy Style" on his hit single from that album "Gin and Juice". His style of slang changed rap, youth culture, and slang in a way that still resonates today.
Scenario: You are quoted a price to fix your car problem for $98, and when you pick up your car they tell you it will be $400.
In this scenario you might want to yell out the the words, "Biatch! You must be crazy!". But because you are more civilized then that, you would actually say the words, "I'm sorry there must be a mistake, I was given a quote of $98 dollars for this job.