History: Ian Thorpe - an Australian Gold Medalist - appeared in advert for a cereal company, a mother who can't get her kids to eat the cereal calls Thorpe up, and asks "What do I do?" to which Thorpe Replies: "Tell them Thorpe says 'Its fully Sick!'"
Usage: It's now used in two ways:
1: When someone does something noteworthy, and ask your opinion, you mearly replies "Thorpe Says..."
2: When someone says a particually unfunny joke, to break up the silence you'd say: "Well... Thorpe said..."
A part of the MSC Dialect