Has nothing to do with the D12 song, but was rather propogated by certain immigrants to a rural, British university community.
"No; I already ate."
"Yes? Well, shit on you!"
2. "What happened to your face?"
"The handlebars fell off my bike, and I nearly died."
"Yes? Shit on this/the bike!"
3. "The Inland Revenue are charging me a million pounds for a mistake they made."
"Shit on them."