A loaf of bread, a jug of wine, and thou.

I was hanging around with a friend chit chatting about this, that, and the other thing.  I don’t remember what we were discussing but she said something about someone having a “wild hair across their ass”.

That’s about as classic a New England-y idiom as you get.  If you haven’t heard the expression, it means that something has happened that has put you in a bad mood and all worked up into a tizzy.

It’s a fairly graphic statement . . . we’re not talking rabbit lying over a donkey’s back.  Use your imagination.

It’s pretty safe to say that if you happened to have a hair lying across your buttocks it wouldn’t be terribly unusual and you  probably wouldn’t notice it under most circumstances.

Perhaps the "wild hair" in the refers to ingrown inflamed perianal hair.  In that case it might cause some discomfort. 

Or if you happen to be particularly hairy . . . uhm . . . back there . . . maybe it refers to the hairs getting knotted.  Consequently, causing difficulty . . . er . . . evacuating the bowel.  That could certainly cause a minor state of panic.

That oughta give you something to think about.