Yeah I didn't really get it either.
Its a scene from the movie, The Amittyville Horror. The nun leaving the house and having to pull over to puke her guts out as soon as she gets a quarter mile down the road always made me laugh cause its so over the top. Maybe I was totally stoned when I first saw it and I being nostalgic?
Sorry, I should know by now my sense of humor is sometimes unique only to myself.