Often referred to as a poo caused by the unnecessary forcing of a fart, shart can also be used to describe a piece of art that one does not find appealing to their eyes/eye. "Shart" in this case is formed by the combination of the adjective "shitty" and the noun "art", which together create: "shitty art".
When Rick came across the popular piece of modern art, he gave his personal opinion on it "What makes this good? Really!? This is just shart! Plain and simple!"