The Governor of South Carolina had an affair with a woman from Argentina. As his cover story he told everyone he was hiking the Appalachian Trail. To sum it up it is slang for having or having had sex.
"Hey have you seen Mark?"
"No but I heard he's with his girlfriend behind the bleachers. They're hiking the Appalachian Trail"**winks**
"Oh that dirty bastard."
Euphemism for preforming oral sex on a woman.
Specifically to lick from the bottom of a woman's labia upwards towards her clitoris.
Mark went 'Hiking the Appalachian Trail' much to the delight of his mistress.
Sneak away to meet your mistress. ("Hiking the Appalachian Trail" is the first explanation of where South Carolina Gov. Mark Sanford was when he disappeared.)
"Has anyone seen Jawann? I've been calling and texting him for three days and he's not answering."
"Uh, he's hiking the Appalachian Trail."
"Oh. Got it."
Refers to someone's infidelity
"Did you hear about Mark's divorce? He was caught hiking the Appalachian trail."
v. To carry on an extramarital affair.
Governor Sanford can't meet with you today; he's "hiking the Appalachian Trail."
To be unfaithful to one's partner e.g. in an extramarital affair. Named after South Carolina Governor Mark Sanford, who was said to be hiking the Appalachian Trail, when actually he was visiting his mistress in Argentina.
"My husband has a lot of "meetings" and "conferences" to attend to lately. I think he might be hiking the Appalachian trail."
cheating on your spouse
I was out "Hiking the appalachian trail"
Making a long-distance clandestine trip for purpose of an extramarital affair
If you can't find me next week, I"ll be hiking the Appalachian Trail.