1. When you are in desperate need of a haircut. 2. When your hair is long, scraggly and in no particular shape. 3. When you have a "hair-jungle" on your head or in your underpants.
Dude walked into the shower sporting quite a hungle, not sure how he gets his girlfriend to go down on that hairy mess, but at least he’s got a 10 inch dick that can escape it.