When a man and a woman are having sex, and when the man is sweaty enough, he scrubs his finger down his ass crack and around the asshole and wipes it under the woman's nose. Or when the woman has not bathed in a long time and her vagina smells really nasty, she fingers it and wipes it under the mans nose.
Paul McCartney gave Yoko Ono the hobo finger last night.
Samantha Ronson gives Lindsay Lohan the hobo finger every day.
It smells like hobo finger in here!