A Quebecois expression for "I don't believe you." It litterally means "my eye." This may mean: "You're full of shit" or "You're shitting me" depending on the context. A dramatic way of displaying this is by putting one's finger below one's eye and pulling the skin below it so you look like a zombie. Kind of like this:

i

The line part of the 'i' (whoa a pun!) being the finger and the dot part being the eye. Here's an example as to how this expression can be used:

somedude: J'ai trouve $500 parterre! (I found $500 on the ground)

me: mon oeil.