A funnel used to fart into peoples mouths, generally any kind of funnel placed into someone's mouth and then farted into, generally it is used on the first person who parties out early.
When someone places their lips tightly around another persons stink trumpet and they fart in your mouth and you swallow that fart like It's grandma's apple pie. Then you belch it back up and blow it in someone's face.
Lester: Hey Jim I need you to give me a good Ol' fart funnel, my grandma pissed me off and now she's gonna regret it.
Jim: say no more my friend! Get ready to suck this fart.