Means that something is very fine, or that you feel excellent. If someone asks how you feel and you simply say "fine", you might just be saying it out of convention. Adding the "dog's hair split three ways" shows that you actually mean it.
Another form of the expression is "finer than a frog's hair split three ways", although literal frogs do not have hair.
Refers to the natural phenomenon that if you have a problem, no matter what it may be, if you go online, someone is selling something to fix your issue.
Person A: I can’t believe someone actually made sleeves for your can if soda!