It does have the connotation of someone who gets wasted and parties while attending these festivals, but the overall meaning is based on simply frequenting festivals.
"So you said Steve might be coming to forest this year?"
"Yeah, but I don't think it's gonna happen, he's not much of a festie."
To go broke in a poker game.
This word was coined by Phil Laak (the unabomber)back in the day when Lucky Chances Casino had a 10/20 NL HE game that
would go around the clock three days a week.
WTF P.O.S. hand could you have had there to get yourself felted again?