A towel is a slag expression for a person that smokes a lot of weed and is pretty obvious about it (so people that secretly
toke once in a while are not towels). Quite simply, a pothead.
Derived from South Park where one minor character who smokes a lot of weed is a
sentient towel.
Sometimes
towie is used instead.
McDonald's employee: "Man, we where just about to close down then a group of fucking towels came in and ordered 50
cheeseburgers..."
Man: "Dude, you're such a
towel..."
Towel: "No,
YOU'RE a towel..."
Man: "No, I am a respectable member of society with a steady job and a loving family. YOU'RE a towel."
Towel: "Oh..."