Wiktionary
happy trail
n. (context slang English) A vertical line of hair that extends up along the middle of a man's abdomen from pubic hair to navel.
Usage examples of "happy trail".
The Happy Trail Getaway was a saloon where the bartender was friendly to the Wolves and the girls were even friendlier, if the words were kind and the price was right, the price being anything from a new pair of shoes to an old song, depending on the charm of the man.