Micro B's occur when your balls become extremely sweaty, smelly and develop a layer of ball cheese that covers the entire circumference of the sack. This is a direct result from a long study session on the 6th floor of the microbial science building due to the heat that fills the room up. Can be cured with a good dip sesh in the showers.
Tyler: "Hey jim why do you smell so bad?"
Jim: "Ahhh bro, youre smelling my micro b's, I have Gen Bus 301 tomorrow with skyler."