Simpy is used as short word when describing a person who is a simpleton. Someone who's mind is so simple, they cannot always grasp concepts. Like a monkey. They also are known as numskulls, blockheads, ninnys, and dopes. A good example of a simpleton would be Jessica Simpson, also known as Jessica Simpleton. You can also use simpy when some one is acting a fool or foolish.
Use simpy as such:
"Melissa, your so simpy!"
"Melissa, your such a simpleton!"
"Melissa, your such a simp!"